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Concept 2.1
Organisms are composed of matter: anything that takes up space or has mass
Element: a substance that cannot be broken down by chemical reactions
Compound: substance consisting of two or more elements in a fixed ratio
Concept 2.1
Life requires about 25 elements4 of those make up 96% of living
matterCarbon, Oxygen, Hydrogen, and Nitrogen
Trace Elements are those that are required in only minute quantities-ex. Iron, iodine
Concept 2.2
Atom: smallest unit of matter that still retains the properties of an element
Subatomic particles: Protons (+), Neutrons (0), Electrons (-)
Protons and Neutrons have a mass of 1 dalton. Electrons have no mass
Concept 2.2
Atomic number: # of protonsMass number: sum of protons +
neutronsIsotopes: different atomic forms of
an element.-ex. Carbon-12 (99%), Carbon-13 (1%), Carbon-14 (<1%)
Concept 2.2
C-12 and C-13 are stable. C-14 is unstable, and radioactive. It will decay giving off particles and energy.
Carbon-14 will decay into Nitrogen
Concept 2.2
An atom’s electrons vary in the amount of energy they possess.
Energy: the ability to do work.Potential Energy: energy that
matter stores because of its position or location
Electrons have potential energy because of their position in relation to the nucleus.
(a) A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons
Third shell (highest energylevel)
Second shell (higherenergy level)
Energyabsorbed
First shell (lowest energylevel)
Atomicnucleus
Energylost
Concept 2.2
Concept 2.2
The different states of potential energy that electrons have in an atom are called energy levels or electron shells.- the first shell has the lowest energy. The second shell has more than the first, etc.
Valence electrons: those in the outermost shell
Concept 2.2Hydrogen
1H
Lithium
3LiBeryllium
4BeBoron
5BCarbon
6CNitrogen
7NOxygen
8O
Fluorine
9FNeon
10Ne
Helium
2HeAtomic number
Element symbol
Electron-distributiondiagram
Atomic mass
2He
4.00Firstshell
Secondshell
Thirdshell
Sodium
11NaMagnesium
12Mg
Aluminum
13AlSilicon
14SiPhosphorus
15PSulfur
16S
Chlorine
17ClArgon
18Ar
Atoms will bond with others to gain stability
Covalent bonds: sharing of a pair of valence e- by two atoms-ex. Hydrogen atoms will share their electrons. They become H-H
Concept 2.3
Concept 2.3
Electronegativity: the attraction of an atom for the electrons of a covalent bond
Nonpolar: when the electrons are shared equally
Polar: when one atom is bonded to a more electronegative atom
Concept 2.3Ionic bonds: when two atoms are
so unequal in their attraction for electrons that one atom will strip the electrons from its partner
Ion: a charged atom; cation has a positive charge, anion has a negative charge (ca+ion; a negative ion)
Compounds formed by ionic bonds are salts
Concept 2.3
Na Cl Na Cl
NaSodium atom Chlorine atom
Cl Na+
Sodium ion(a cation)
Cl–Chloride ion
(an anion)
Sodium chloride (NaCl)
The advantage of weak bonding is that the contact can be brief
Hydrogen bonds: H is covalently bonded to an electronegative atom and attracted to another electronegative atom.-ex. Water and ammonia
Concept 2.3
Concept 2.4
Chemical reactions: making and breaking of chemical bonds.- starting material is reactants- ending material is products
Chemical equilibrium: point at which reactions offset one another.