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Matter!Matter is anything that occupies space and has
mass.
Will this astronaut occupy the same space on the moon as he does on Earth?
Will this astronaut weigh the same on the moon as he does on the Earth?
Mass and weight are not the same.
The Atom –The Simplest of Particles
• The atom is the simplest particle of an element that retains the properties of that element.
The Structure of an Atom Bohr Model – “planetary model”• Proposed by Niels Bohr in 1915• A useful approximation of the structure of
an atom.Consists of two parts:• A central region, or nucleus• Electron cloud – composed of orbitals or
three-dimensional regions around a nucleus
Subatomic ParticlesProtons Positively (+) charged particles Have mass (1 amu = 1 atomic mass unit) Located in the nucleus
+
Neutrons Neutral particles (No charge) Have mass (1 amu) Also located in the nucleus
n
Electrons Negatively (-) charged particles Mass is negligible (1/1840 amu) Remain in constant motion in orbitals
The Bohr ModelBelow is a Bohr Model of a helium (He) atom.
n +n+
Nucleus 2 protons2 neutrons
Electron cloudConsists of orbitals where high-energy electrons orbit the nucleus
Elements
• Elements are substances that cannot be broken down chemically into simpler kinds of matter.
The Elemental Body --The Major Elements
Rank
Chemical
Symbol
Element% of
human body*
1 O Oxygen 62 %
2 C Carbon 23 %3 H Hydrogen 10 %4 N Nitrogen 2.6 %5 Ca Calcium 1.4 %6 P Phosphorus 1.1 %7 K Potassium 0.2 %8 S Sulfur 0.2 %9 Na Sodium 0.1%10 Cl Chlorine 0.1 %11 Mg Magnesium 0.02 %* Based on an average 70 kg (154 lbs.) person
A major element is any element that makes up more than 0.01% of your body mass.
The Elemental Body --The Trace Elements
A trace element is any element that makes up less than 0.01% of your body mass, but is still critical to your health.
Rank
Chemical
Symbol
Element
12 Fe Iron13 F Fluorine14 Zn Zinc15 Si Silicon16 Cu Copper17 I Iodine18 Sn Tin
Rank
Chemical
Symbol
Element
19 B Boron20 Se Selenium21 Cr Chromium22 Mn Manganese
23 Mo Molybdenum
24 Co Cobalt25 V Vanadium
Atomically Speaking…• The number of protons in an atom is called the
atomic number.• In an atom, the number of positive protons is
balanced by an equal number of negative electrons. – net electrical charge equals zero
The Bohr model to the left represents an atom of which element?
How many electrons must be in the electron cloud?
= neutron = proton
Atomically Speaking…
• The mass number of an atom is equal to the total number of protons and neutrons of the atom.
What is the mass number of our carbon atom?
= neutron = proton
Isotopes: Not All Atoms are Created Equal
Isotopes are atoms of the same element that have different numbers of neutrons.– therefore they will have different mass numbers– this is the reason for the average atomic mass in the periodic table
= neutron = proton
Click here to compare these two atoms.
These two atoms are both carbon atoms. But the atom on the left has 6 neutrons while the atom on the right has 7 neutrons. Because of this, these two atoms are said to be isotopes of one another.
These two atoms are both carbon atoms. But the atom on the left has 6 neutrons while the atom on the right has 7 neutrons. Because of this, these two atoms are said to be isotopes of one another.
CLOSECLOSE
Radioactive Isotopes
• Sometimes having too many neutrons can make the nucleus of an atom unstable.– Unstable nuclei decay, or break apart.– Particles (usually neutrons) and energy in the form of
radiation are released.– This radiation can be used to calculate the age
of an object or it can be used in medical treatments such as radiation therapy.
A Few Words About Electrons
• High energy particles• Are attracted to (+)ve protons in the nucleus – keeps
them close together• Constant energy of motion prevents them from
collapsing into nucleus• Exact path of travel cannot be known• An electron’s energy confines it to an energy level
within the electron cloud• Electrons with higher energy occupy energy levels
farther from the nucleus
Orbitals• Energy levels contain orbitals which can only
hold a certain number of electrons.
Energy Level
# of orbitals
Maximum # of
electrons1 1 2
2 4 8
3 9 18
Expanding the Bohr ModelExample: A carbon atomWe know:
From periodic table • atomic number of carbon equals six;• therefore the number of electrons equals six Why?
From previous chart• first energy level holds two electrons maximum• second energy level holds eight electrons maximum
= neutron = proton = electron
Expanding the Bohr ModelPutting it all together:
Two of carbon’s electrons will be found in the first energy level of the electron cloud.
The remaining four electrons will be found in the second energy level of the electron cloud.
The second energy level of a carbon atom is not full. It can still accommodate four more electrons.
Compounds
• Compound – substance formed when two or more different elements combine– Form a specific combination of elements in a fixed
ratio– Chemically and physically different from the
elements that comprise them– Cannot be broken down into simpler compounds
or elements by physical means (can be broken down chemically)
Why Combine?
Compounds form because most atoms are not stable in their natural state.
A partially-filled outermost energy level is not as stable as an energy level that is completely filled with the maximum number of electrons it can hold.
Is this carbon atom stable?
= neutron = proton = electron
Chemical BondsIonic Bond Covalent Bond
An atom can gain or lose an electron to make a stable energy level. This atom is called an ion and is now charged.
An ionic bond is electrical attraction between two oppositely charged atoms.
Example: sodium chloride
A chemical bond that forms when electrons are SHARED
Example: water
Achieving Stability
Atoms become stable by attaining at least one of the following:– They fill their outermost, or valence, energy level
with the maximum amount of electrons that it will hold.
OR– They fill their outermost energy level with eight
electrons.• The ‘Rule of Eight’
There IS Another Way
Atoms can also share one or more pairs of electrons. – When two atoms share electrons, the shared electrons
occupy orbitals around both of the atoms.– The electrons move so quickly that it is difficult to predict
which atom they are orbiting at any given time.
Water – A Model of Covalent Bonding
Hydrogen1 p0 n
Oxygen8p8n
Hydrogen atom (atomic #: 1) Oxygen atom (atomic #: 8)
How many valence electrons does each atom have?
How many more electrons does each atom need to fill its outermost energy level?
Water – A Model of Covalent Bonding
Hydrogen1 p0 n
Oxygen8p8n
Hydrogen1 p0 n
This is a molecule of water. It can also be referred to by its chemical formula, H2O.
A shared pair of electrons can be considered to be part of the outermost energy level of both atoms that share them.
This is a molecule of water. It can also be referred to by its chemical formula, H2O.
A shared pair of electrons can be considered to be part of the outermost energy level of both atoms that share them.
How might each of these atoms fill its outermost energy level?
Hydrogen1 p0 n
Oxygen8p8n
If each hydrogen atom shares a pair of electrons with oxygen, how many valence electrons does each atom have?
Covalent BondA covalent bond forms when two atoms
share one or more pairs of electrons.– A molecule is the simplest part of a substance
that retains all the properties of that substance
Modeling Ionic Bonds
Activity In your notes, draw a Bohr model of a
sodium atom (atomic number 11). Next to the sodium atom draw a Bohr model of a chlorine atom (atomic number 17).
Activity
1. On the left, draw a neutral sodium atom with a mass number of 23 (atomic number 11).
2. On the right, draw a neutral chlorine atom with a mass number of 35 (atomic number 17).
The Sodium-Chlorine Ionic Bond
Sodium11 p12 n
Chlorine17 p18 n
Sodium atom (atomic #: 11) Chlorine atom (atomic #: 17)
How many electrons does each atom have now?
How does this affect the total charge of each atom?
The Sodium-Chlorine Ionic Bond
Sodium11 p12 n
Chlorine17 p18 n
These atoms are no longer electrically neutral.
Protons +11Electrons -10Charge +1
Protons +17Electrons -18Charge -1
These atoms are stable, but because of their opposite charges they now attract one another.
How many protons does sodium (Na) have?
How many electrons does Na have now?
What is the total charge of this atom of sodium?
The Sodium-Chlorine Ionic BondAn atom with an electrical charge is called an ion. As a result of their opposite charges, sodium ions and chlorine ions attract each other.
Sodium11 p12 n
Chlorine17 p18 n
Sodium ion +1
Chlorine ion-1
An ionic bond is the chemical bond formed between ions with opposite charges.
This new substance is a compound called sodium chloride.
Chemical Reactions
• Process by which atoms or groups of atoms in substances reorganize into different substances
• Chemical bonds are broken or formed
• For example – 4 Fe + 3 O2 2 Fe2O3
Reactants and ProductsChemical Equation:
C6H12O6 + O2 CO2 + H20
(Glucose and oxygen react to form carbon dioxide and water)
Reactants (starting substances):C6H12O6 + O2
Products (substances formed):CO2 + H20
Balanced Equation• According to the principle of conservation of
mass, matter cannot be created or destroyed• The number of atoms of each element on the
reactant side must equal the number of atoms of the same element on the product side
For example:
2 H2O2 2 H20 + O2
C6H12O6 + 6 O2 6 CO2+ 6 H20
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