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SNC1D EXAM STUDY
SHEETS
Sustainably, electrostatics and chemistry (part A)
2
Table of contents
Sustainability .................................................................................................................................................
Introduction to ecosystems .................................................................................................................... 3
The biotic components of ecosystem .................................................................................................... 4
Recycling of matter ............................................................................................................................... 5
The abiotic components of an ecosystem ............................................................................................. 6
The nitrogen cycle ................................................................................................................................ 7
Habitat, niche and competition ............................................................................................................. 9
Population ecology ............................................................................................................................... 9
Electrostatics .................................................................................................................................................
Introduction to electrostatics ............................................................................................................... 10
Transferring electric charge ................................................................................................................ 12
Insulator/conductor ............................................................................................................................. 14
Definitions and terms .......................................................................................................................... 15
Chemistry.......................................................................................................................................................
Matter and the particle theory ............................................................................................................. 17
Pure substances and elements ............................................................................................................. 17
Structure of the atom, isotopes ,Bohr diagram and ions ..................................................................... 18
The Rutherford-Bohr diagram atom and chemical families ............................................................... 19
Compounds ......................................................................................................................................... 19
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SUSTAINABILTY
INTRODUCTION TO ECOSYSTEMS
The earth is a big ball of rock with a molten core. On the surface of this rock, we find water, air and
soil. And in, on and around this water, air and soil, we find life. Animal life, plant life, and
microscopic life.
Life: The condition that distinguishes organisms from inorganic and dead organisms, being
manifested by the growth through metabolism, reproduction, and the power of adaptation to
environment through changes originating internally.
This thin layer of lie on the surface of the Earth is called the biosphere (“bio” means living).
Lithosphere: the solid parts of the Earth including rocks, soil and even ice.
Hydrosphere: the liquid parts of the Earth including lakes, oceans, rivers, etc.
Atmosphere: the gas and vapour surrounding the Earth.
The interaction of all the organisms in the biosphere with each other and with their environment is
called ecology.
The study of all the interactions in the biosphere is so impossibly big and complex, biologists and
ecologists have separated the surface of the Earth into various regions called biomes.
A biome is defined as a region of the Earth with a particular climate which has a controlling effect on
the types of plants and animals found there. The largest Canadian biomes include the tundra, the
boreal forest (taiga), the temperate deciduous forest, the grasslands, and the mountain biome.
An ecosystem is defined as a grouping of plants, animals, and other organisms interacting with each
other and their environment. Example: meadows, ponds, cities, etc.
An ecosystem involves both living factors and non-living factors. The living factors are called biotic
factors and the non-living factors are called abiotic factors.
The biotic factors are often very dependent on the abiotic factors. The abiotic factors can greatly
affect an organism’s ability to survive in an area. This is sometimes referred to as the range of
tolerance for an organism.
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THE BIOTIC COMPONENTS OF ECOSYSTEMS
All these factors (biotic and abiotic) play important roles in the survival and sustainability of the
ecosystem.
Plants, called producers, are able to produce their own food from the abiotic environment (water,
CO2 (carbon dioxide) and sunlight).
Since they can “feed themselves, they are referred to as autotrophs.
This process of making their own food is called photosynthesis.
Photosynthesis takes place in a series of chemical reactions that take place inside the plant cells.
REACTANTS PRODUCTS
Carbon dioxide + water + light Glucose (sugar) + oxygen
CO2 + H20 + light C6H12O6 + O2
The plants then store this food (sugar) in the form of starch, resulting in growth of the plant, or use it
themselves as a source of energy for their own cells.
The process of breaking apart glucose to release energy for cells is called cellular respiration. Again,
this involves a long series of chemical reactions but can be summarized into the following equation:
REACTANTS PRODUCTS
Glucose (sugar) + oxygen Carbon dioxide + water + energy
C6H12O6 + O2 CO2 + H20 + energy
Both animals and plants use cellular respiration to supply usable energy for their cells.
The animals and microbes, called consumers, rely on plants and other animals for their food energy.
Because consumers require other organisms as their food source, they are referred to as heterotrophs
(eat others).
Herbivores: heterotrophs that eat only plants
Carnivores: consumers that eat only other consumers
Omnivores: those that eat both plants and animals
Decomposers: consumers responsible for breaking down dead material and waste products.
All consumers ultimately rely on plants; plants are an essential part of all ecosystems. Plants could
not survive without animals and microbes... (Supplying minerals in the form of waste products, seed
dispersion, CO2, etc) and of course the abiotic factors (soil, water, sunlight, etc).
All components work together to maintain and sustain a healthy ecosystem. Almost all ecosystems
have a diverse variety of plants, animals and microbes interacting with each other and their
environment.
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The greater the number of plants, animals, and microbes, the greater the biodiversity. If biodiversity
is reduced, this may impact and damage the ecosystem. Ex. Cutting and burning the rainforests, over
fishing, hunting, etc.
Biodiversity: Existence of a wide variety of plant and animal species in their natural environments.
RECYCLING OF MATTER
When the biotic and abiotic components depend on each other, it results in a constant flow of material
from component to component: a sort of natural recycling.
This is necessary because Earth is a closed system. This means that although we have many different
types of atoms (H, O, C, N, etc), we only have a limited quantity of each and we are not getting
anymore.
There is a finite (limited) amount of all matter on Earth so this natural recycling is necessary or we
would run out of some form of matters, resulting in problems.
This constant recycling of atoms and molecules is necessary for all living things. All the atoms have
been in countless other organisms before. Although we are all unique, we are completely recycled
material.
All the atoms in us have been in countless other organisms before. We are completely recycled
material.
THE ABIOTIC COMPONENTS OF AN ECOSYSTEM
The abiotic components in an ecosystem are often the controlling factors, determining the types of
plants, and animals that can survive in that particular ecosystem.
For example, in a desert ecosystem, the amount of sunlight, temperature range (day-night), rainfall (or
lack of), and soil conditions are some of the controlling abiotic factors. These will all play major roles
in determining what species of plants can survive, and thus affects all the other biotic components as
well.
Most plants & animals have a certain range of conditions in which they can survive (called range of
tolerance). If the conditions change beyond their range of tolerance, the organism will not be able to
survive for any extended period of time.
For example, if you don’t supply a house plant with enough water, what will happen to it? What
about if you over-water it? All living things have specific ranges of tolerance for difference abiotic
factors.
Often you will find certain species (plants or animals) within a particular ecosystem but not others.
The reason for this is that the organism probably confronts one or more abiotic factors which are
limiting to its survival.
Soil is usually considered to be an abiotic factor affecting the different plants and animals in the
ecosystem. Soil, itself, can be an ecosystem with abiotic factors (minerals, water, air, etc) and biotic
factors (bacteria, fungi, insects, plants, etc).
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Rich topsoil contains a complex combination of mineral particles, organic matter from dead
vegetation and animal wastes in various stages of decomposition. As well, decomposers (bacteria and
fungi), earthworms, snails, and insects can be found, helping to break down the larger particles, and
helping with the recycling process.
Rich topsoil contains a complex combination of mineral
particles, organic matter from dead vegetation and animal wastes in various stages of decomposition.
As well, decomposers (bacteria and fungi), earthworms, snails, and insects can be found, helping to
break down the larger particles, and helping with the recycling process.
In nature, bedrock breaks apart forming parent material (also called regolith), and this breaks down
further to form the subsoil. Plants require mineral nutrients such as nitrates (NO3), phosphate (PO4),
potassium (K), and calcium (Ca) to be able to grow properly.
Some of these nutrients come from broken down rocks and some come from decomposing matter in
the humus layer. Excess water can result in these minerals being washed down into the eluviation
layer, a process called leaching.
Farmers often add fertilizer to the soil to replace the nutrients that the plants have used up. This can
be in the form of animal wastes (manure) or chemical fertilizer.
If too much fertilizer is applied to the fields, the excess can run off into nearby bodies of water. This
excess fertilizer can result in rapid growth of algae (an aquatic plant) which can quickly damage the
ecosystem. This result is called an algal bloom.
Other activities that can influence an aquatic ecosystem include use of pesticides and herbicides,
industrial pollution, and urban development.
7
BIOACCUMULATION
Other activities that can influence an aquatic ecosystem include use of pesticides and herbicides,
industrial pollution, and urban development.
Food chains and food webs are methods to follow the feeding sequence in an ecosystem. They
illustrate the flow of energy and materials from one organism to the next through the ecosystem. A
food chain can also be used to show how some ecological problems occur.
For example: Dan buys a herbicide (weed killer) that has been thoroughly tested and proven safe at
the concentration it is to be used at. He sprays his crop and all seems fine. Each blade of grass absorbs
1 molecule of this chemical…perfectly safe! A grasshopper eats 100 blades of this grass so it now has
100 molecules of this chemical in it’s’ body. Let’s say this is still safe. A frog eats 100 grasshoppers.
It would now have 10 000 molecules of this chemical in its body. A fish eats 100 frogs, and so on…
Notice as we go further along the food chain, the concentration of the chemical is increasing to a
point where it could easily become toxic. And remember, humans are at the end of many food
chains!! This process is known as bioaccumulation and can severely damage a food chain and
ecosystem.
THE NITROGEN CYCLE
One example of the cycling of matter can be seen in the Nitrogen Cycle. Nitrogen is necessary in the
construction of proteins, DNA (genetic material), and other molecules necessary for life.
Nitrogen gas (N2) makes up approximately 79% of the atmosphere. Unfortunately, it is a very stable
and not readily useable.
Converting nitrogen gas into a more useable form (called nitrate NO3-) is known as nitrogen
fixation. There are two ways for nitrogen fixation to occur: lightning or bacteria in the soil.
The large amount of energy released by lightning can cause nitrogen to react with the oxygen in the
air, forming small amounts of nitrates. These nitrates then dissolve with rain or surface water and
move into plants by their roots (entering the biotic components of the ecosystem).
The plants can then use these nitrates to make DNA and/or proteins that can be taken into consumers
when the plants are eaten. Some bacteria in the soil are capable of fixing nitrogen, the main way of
supplying nitrates to ecosystems.
Some of these nitrogen-fixing bacteria can be found in small lumps (called nodules) on the roots of
certain plants (called legumes). Ex. clover, soybeans, peas and alfalfa.
The bacteria create more nitrates than the plants can use, so some remains in the soil for other plants.
Often, when farmers are growing crops, they will plant a field for a season with a legume, to increase
the amount of nitrates in the soil for the next year’s crops.
Nitrogen, once in the biotic environment, will eventually return to the abiotic environment, usually in
the form of waste products or dead organisms. Bacteria in the soil break down the nitrogen-containing
chemicals into simpler chemicals called ammonia (NH3).
Other bacteria convert ammonia into nitrites, and still other bacteria convert nitrites into nitrates,
which can again be used by plants. When farmers fertilize their fields, or we fertilize our lawns, we
8
are adding manure or other chemicals which contain ammonia, which again gets converted into
nitrates for the plants.
There are also denitrifying bacteria that can convert nitrates into nitrites and back into nitrogen gas
which is released into the atmosphere. This process is called denitrification, and is carried out by
bacteria that do not require oxygen.
When homeowners aerate their lawns, they are allowing oxygen into the soil, limiting the effect of
these denitrifying bacteria, allowing the nitrates to remain in the lawn for better grass.
These denitrifying bacteria help to maintain the balance between nitrates, nitrates and N2 gas in the
atmosphere, and help to create the cycling of nitrogen.
Some plants, like the venus-fly trap, pitcher plant, and the sundew live in areas (swamps and bogs)
where there is very little nitrate in the soil. They have adapted to this type of environment by getting
their nitrogen from a different source...they use the proteins and DNA from insects that they catch.
9
HABITAT, NICHE AND COMPETITION
All species require a habitat and a niche. An organism’s habitat is where it lives. Ex. A deer’s habitat
is the forest.
An organism’s niche is how the organism fits into its ecosystem, all the ways it interacts with both the
biotic and abiotic environment.
Ex. A deer’s niche would be to: eat grass and leaves, take in O2, produce CO2, fertilize the soil,
provide blood for mosquitoes, provide food for wolves, etc.
When two different species share the same habitat and the same niche, competition occurs. They are
competing for the same food source and territory. This can be a good thing because it keeps both
species’ populations under control. This allows for a more diverse food web and ecosystem.
Sometimes, a new species will get into an ecosystem from a completely different ecosystem. This is
referred to as an invasive species. Because this new species has no natural predators in the
ecosystem, the invasive species can out-compete the native species, and can lead to changes in the
ecosystem.
POPULATION ECOLOGY
Ecosystems are composed of communities which are made up of populations of species.
Species: a group of similar individuals who can mate and produce viable (living), fertile (able to
reproduce) offspring.
Population: a group of similar individual (same species) who live in a limited geographic area.
Community: the relationship between groups of different species in an area.
The carrying capacity of an ecosystem is defined as the maximum number of individuals that can be
supported by an ecosystem without damaging that ecosystem. If carrying capacity is exceeded, the
ecosystem may be damaged beyond repair.
There are a number of factors that can affect the size and rate of growth of a population. Ex. available
food, available space, water, reproductive rate, predators, natural disasters, human influence, etc.
Given normal conditions, and no drastic outside factors, a population will tend to reach an
equilibrium and remain fairly constant. This equilibrium allows most ecosystems to become stable
and self-sustaining.
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Even looking at the interactions between predator and prey, we can see a relationship between the
population sizes.
An open population is one in which organisms may enter (immigrate) or leave (emigrate). A closed
population is one in which they cannot. Ex. an island.
Four factors that affect the rate of growth of a population:
Immigration, Emigration, Birth, Death.
ELECTROSTATICS
LESSON: INTRODUCTION TO ELECTROSATICS
- All matter is made up of atoms which are in turn made of particles which have electric charges.
- If an object has no electric charge, it is said to be neutral.
- Two electrically uncharged objects will have no affect on each other.
- An electrically charged object exerts a force on a neutral object, even if they are not touching.
- Electric charges can be either positive or negative.
- Like (the same) charges repel and unlike (different) charges attract.
- This is known as the Law of Electric Charges.
- According to the Rutherford-Bohr Model of the atom, the nucleus of an atom contains positively
charged protons and neutral neutrons.
- Around the nucleus at different energy levels are found the negatively charged electrons.
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- Because the electrons are found at various energy levels (sometimes called shells or orbitals), they
can often be removed easily from an atom whereas the protons and neutrons are trapped in the
nucleus.
- Any transfer of electric charge involves the movement of electrons from one object to another.
- Because the electric charge on an object will often remain for long periods of time, the electricity is
called static electricity (stationary).
- The science of studying static electricity is called electrostatics.
- To determine whether or not charge has been transferred, a device called an electroscope can be used.
This will respond to charged objects but not to uncharged objects.
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LESSON: TRANSFERRING ELECTRIC CHARGE
- There are 3 methods by which objects can gain an electric charge (become charged):
1. friction
2. contact
3. induction
1. Charging By Friction
- Some substances have a strong hold on their electrons and others have a weak hold.
- As a result, when two substances are rubbed together, the substance which has a weak hold on its
electrons will lose some its electrons (and become positively charged).
- The substance which has a stronger hold on its electrons will gain some electrons (it will become
negatively charged).
- When charging by friction, both objects start out neutral and one becomes positive and the other
becomes negative.
- A table was set up called the Electrostatic Series (see the list)
- It is a list of substances showing which ones have a strong hold on their electrons (and will steal
electrons from other substances) and become negatively charged and which have a weak hold on their
electrons (and will lose electrons) and become positively charged.
2. Charging by Contact
- When a charged object comes in contact with a neutral object, there is a transfer of electrons from the
object with the most electrons to the other object.
- This often creates a spark (a shock) as the electrons jump to the other object.
- The other object always receives the same charge as the object that touched it.
- When charging by contact, both objects end up with the same charge as the charging object.
3. Charging By Induction
- If a negatively charged rod is brought near a neutral object, the electrons in the neutral object will be
repelled and the side of the neutral object near the negatively charged rod will become positively
charged and will be attracted.
- If the neutral pith ball is touched on its negative side using another neutral object or wire (called a
ground), the electrons will move over to the new object, leaving the pith ball positively charged.
Notice that the negative rod never touched the pith ball!
Notice that we have given a pith ball a positive charge using a negatively charged rod.
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CHARING BY INDUCTION
CHARING BY CONTACT
NEGATIVE
POSTIVE
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LESSON: INSULATOR/CONDUCTOR
- An insulator is a substance in which electrons cannot move easily from atom to atom.
- If the atoms do gain extra electrons, the electrons remain with the atom until they are removed.
- A conductor is a substance in which electrons can move easily from one atom to another.
- If a conductor gains extra electrons, they move freely along the surface.
- To discharge or neutralize the charge on an object, the object is connected to a conductor which
conducts the excess electric charge away from the object.
- This is often done by connecting the object to the Earth (called grounding), which is a good conductor
and removes the excess electrons.
ELECTROSERIES (TRIBOELECTRIC)
Human hands (usually too moist, though) Very positive
Rabbit Fur
Glass
Human hair
Nylon
Wool
Fur
Lead
Silk
Aluminum
Paper
Cotton
Steel Neutral
Wood
Amber
Hard rubber (ebonite)
Nickel, Copper
Brass, Silver
Gold, Platinum
Polyester
Styrene (Styrofoam)
Saran Wrap
Polyurethane
Polyethylene (like Scotch Tape)
Polypropylene
Vinyl (PVC)
Silicon
Teflon Very negative
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DEFENITONS AND TERMS
Neutral: when an object has no electric charge.
No affect: What two electrically uncharged objects will have on each other.
Law of Electric Charges: When like charges repel and unlike charges attract.
Like: same
Unlike: different
Rutherford-Bohr Model: A model of an atom.
Neutrons: particles inside of the nucleus; neutral. The Rutherford-Bohr Model
Protons: positively charged particles, found in the nucleus (see P.D.M)
Electrons: negatively charged particles, found around the nucleus.
Energy levels/shells/orbitals: the level of energy of an electron, also the distance between the electron to
the nucleus ( not 100% sure on that).
P.D.M: PROTONS DON’T MOVE!!!!! BIGGGIEEEE!
Static electricity: when the electric charge on an object remains for long periods of time; stationary.
Electrostatics: The science of studying static electricity.
Electroscope: a device to determine whether or not charge has been transferred; will respond to charged
objects but not to uncharged objects.
Charging by Friction: When you start out with two neutral objects, and you rub them together. One
becomes positively charged, while the other becomes positively charged, because one is losing while the
other is gaining electrons.
Positively charged: When the substance loses some electrons.
Negatively charged: When the substance gains electrons.
Electrostatic series: a list of substances showing which ones have a strong hold on their electrons, and
which have a weak hold on their electrons.
Spark: a shock.
Ground: another neutral object or wire that connects somehow to the ground, either sending in or sending
out electrons.
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Charging by Contact: When a charged object comes in contact with a neutral object, creating a transfer
of electrons from the object with the most electrons to the other object (often creating a spark).
Charging by Induction: When a neutral object is brought near a charged object, then grounded, and the
ground is removed, without the charged object touching the neutral object.
Grounding: when you connect the charged object to the Earth.
Discharge/neutralize: when you connect the object to a conductor which conducts the excess electric
charge away from the object, or conduct electrons in.
Conductor: a substance in which electrons can move easily from one atom to another.
Insulator: a substance in which electrons cannot move easily from atom to atom.
Lightning rod: a metal rod or wire attached to a building to prevent lightning damage by conduction the
electrons to the ground.
Electrostatic precipitator: a device to control air pollution using stationary electric charges.
Thunder: The sound made by lightning.
Lightning: in the sky, a flash of bright light caused by the discharge of electricity between clouds, or
between clouds and the ground.
Static cling: the tendency for objects to stick/cling to other objects, when the two objects are oppositely
charged.
Electrostatic spray painting: spray painting by charging the object being painted positively, and
spraying it with negatively charged paint leaving the nozzle, attracted to the positive target. Gives a
smooth thin layer of paint, and ensures that the surface is thoroughly covered.
Van de Graaff generator (VDG): an electrostatic generator.
17
CHEMISTRY
Matter and the Particle Theory
- Matter is anything that has mass and takes up space.
- To determine what type of matter something is, we use our senses and we make observations about
the matter.
- These observations are called properties.
- We study the properties of matter to determine how it behaves and this helps us to know how to deal
with the matter.
- All matter has certain things in common and these have been combined together to form the Particle
Theory of Matter.
- The Particle Theory of Matter helps us understand about the properties of all types of matter.
The Particle Theory of Matter
All matter is made up of small particles.
All particles of a pure substance are identical to each other and different from another pure
substance.
All particles are constantly moving.
Particles attract each other.
Particles at higher temperatures (more energy) move faster than particles at lower temperatures.
Pure Substances and Elements
- Matter can be classified into two categories: pure substances and mixtures.
- A pure substance is composed of only one substance, unlike mixtures which can be a combination of
many pure substances.
- Any sample of a pure substance would have the same composition and properties
- There are two forms of pure substances: elements and compounds
- Pure substance: A substance is pure only if it has the same composition throughout the sample.
- It’s components cannot be separated by physical methods.
- Element: pure substance that cannot be broken down into simpler substances by ordinary physical or
chemical means. They are the basic building blocks of all matter.
- Each element has its own characteristic proprieties.
- Smallest thing an element can be dvided up into is an atom.
- With the exception of mercury, most of the 118 elements are classified as metals (shiny an good
conductors), and are solid.
- The other elements are classified as the non metals.
- Many are gasses at room temperature.
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- Each different element has a chemical symbol/abbreviation, consisting of a single/2 letters (some
have 3), the first in which is always capitalized. Eg. Hydrogen = H, Sodium = Na.
Structure of the Atom, Isotopes, Bohr Diagrams and Ions
- An atom has a nucleus which contains positively charged particles called protons, and neutral
particles called neutrons.
- Electrons are negatively charged particles, surrounding the nucleus.
- it takes 1,836 electrons to equal the mass of one proton.
- Protons and neutrons are the same mass/size (about).
- The atomic number is the number of protons in an atom. Eg. Hydrogen (H) 1, Gold (Au) 79.
- The atomic mass of an element is the sum of protons and neutrons in the nucleus.
- Subtract the atomic number from the atomic number to find the number of neutrons.
- A neutral atom has the same number of protons and electrons.
- Eg. Carbon (C) is number 6 (atomic number). That means it has six protons and 6 electrons…. The
atomic mass is 12 so that means it has 6 neutrons (12-6=6).
- Although all the atoms of an element have the same number of protons (same atomic number), they
may have different numbers of neutrons.
- Atoms with the same number of protons but a different number of neutrons are called isotopes.
- Electrons circle around the nucleus, and they are found at certain energy levels/shells (each shell is a
different distance from the nucleus). Atoms have layers.
- The first energy level can hold a maximum of 2 electrons. The 2nd
energy level can hold 8, the 3rd
hold 18 and the 4th holds 32 electrons. (MAXIUM OF EACH).
- The closest energy gets filled first (2), then builds outwards.
- The diagram of the atom showing the electron arrangement is called a Bohr diagram (Neils Bohr).
- When energy is added to the atom (eg. heat), the electrons absorb some of this energy and become
excited and may jump to a higher energy level.
- When the electron returns to its normal energy level, the extra energy is released in the form of light.
- Different elements require different amounts of energy to move the electrons.
- The number of electrons and protons are usually balanced resulting in neutrally charged matter.
- If an electron is removed from an atom, the atom becomes positively charged (and is called a cation)
(it has lost some of its negative charge).
- If it gains one or more extra electrons, it becomes negatively charged (called an anion).
- An atom with a positive/negative charge is called an ion.
19
The Rutherford-Bohr Model of the Atom and Chemical Families
- The Rutherford-Bohr Model is the model of which the electrons are around the nucleus and the
protons and neutrons are in the nucleus.
- Atoms are very small.
- The mass of an electron is extremely small compared to the mass of the entire atom.
- The electrons exist in energy levels outside the nucleus.
- Atoms are made of charged particles that can be separated from each other to form ions.
- The identity of an element is determined by the number of protons in the nucleus.
- Atoms of the same element can differ only in the number of neutrons in the nucleus.
- The periodic table is also organized by atomic number and the number of electrons in their outermost
energy level, called the valence shell electrons.
- Each column represents a group of elements that have similar properties, and they are called families.
- They are in the same family because they have the same number of valence shell electrons and this
determines their chemical properties (what they react with).
- 1st column except for hydrogen is called the Alkali metal Family, which has 1 electron in their
valence shell. They will react with water explosively, and they are shiny &s soft metals.
- The second column (Be, Mg, Ca… ) is called the Alkaline Earth Metal Family. They are very
reactive and only found natruall in compounds.
- The 17th column (group 7… F, Cl, Br….) is called the Halogen Family. Halogen means salt former
and all compounds with halogen elements are salts. They also kill germs when dissolved in water.
- The last column (18th column groupe 8, He,Ne,Ar…) is called the Noble/Nobel Gases family. They
are completely filled (the valence shell) and they will not readily combine with other elements to
form compounds. When electricity is passed through the gases, light is released.
Compounds
- When two or more elements combine together chemically to form a compound, the atoms are held
together by stored energy called bonds.
- When a compound forms, it has very different properties than the original elements.
- Eg. Na + Cl NaCl
- Na (explosive metal) + Cl (Poisonous gas) = salt (tasty food additive)
- There are two types of compounds formed when atoms come together and bond: ionic compounds
and molecular compounds.
- Ions are atoms with a charge.. either they have lost/gained electrons (P.D.M).
- Metals always lose electrons to make their outer energy level become stable
- Eg. Na (atomic number 11) has an electron arrangement of 2,8,1. The sodium atom will give away
it’s one valence electron so that it appears to have a stable outer energy level (8) and the atom ends up
with a charge of +1 (one more proton than electrons). A sodium ion is written as Na+1
or Na+.
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- Eg. Mg with an electron arrangement of 2, 8,2 will lose its two outer electrons and become Mg+2
.
- Non-metals always gain electrons to make their outer energy level stable.
- Eg. Cl (atomic number 17) has an electron arrangement of 2, 8, 7. It will gain 1 electron to produce a
stable outer energy level and the atom ends up with a charge of -1 (one more electron than protons).
A chlorine ion is written as Cl-1
or just Cl-.
- Metal ions are always positive and non-metal ions are always negative. A positive charge on a metal
ion will attract the negative charge on a non-metal ion and the two ions will stick (bond) together,
forming an ionic compound. This attraction is called an ionic bond.
- The charges almost always balance out so an ion with a charge of +1 (Na+) will attract an ion with a
charge of -1 (Cl-) to produce a balanced (stable) ionic compound (NaCl).
-
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- An ion with a charge of +2
can attract an ion with a charge of -2
or two ions with a charge of -1
.
Ca+2
+ 2Cl- →CaCl2
- Whenever a chemical reaction is written, the starting substances (called the reactants) are written
first, followed by an arrow (→), and then the resulting substances (called the products).
Eg. Mg+2
+ O-2
→ MgO
- One method used to find the chemical formula for the product at the end of the reaction is called the
Criss Cross Method: Write the symbol for the elements and then put their charge above each one.
Then forget the signs (+/-) and crisscross the numbers.
2 1
Mg F = MgF2
- This crisscross method also works when forming molecular compounds. Molecular compounds are
formed when two non-metals bond together by sharing one or more pairs of electrons (called
covalent bonds).
- H2 gas, N2 gas, O2 gas, CO2 are diatomic molecules – (since 2 of the same atoms bonded together).
- When writing the name of ionic compounds, the metal element name always comes first and the non-
metal element name is changed to end in “ide”.
- Eg. Na+ + Cl
- → NaCl
- Sodium + Chlorine → Sodium Chloride
- Eg. K+ + N
-3 → K3N
- Potassium + Nitrogen → Potassium nitride