1. All Living Things are made of Matter
Chemistry Review
All Living Things are made of Matter

2. Biology Basics
All living things are made of atoms and their interactions.

3. All Matter is Composed of Atoms
neutron
proton +
The atom is composed of
A nucleus made of neutrons and protons
An electron “cloud” composed of electrons
Representation of a nucleus
Protons and neutrons have nearly identical masses, but their charge is different
Protons have a positive (+) electrical charge and neutrons do not have an electrical charge 3

4. Subatomic Particles Composing the Atom
Charge
Size
Location
Proton +1 1
Part of the nucleus
Neutron
Electron -1
Electron “cloud”
(outside of the nucleus) 4

5. Red dots represent areas of probability
The Quantum Atom
We can only describe areas of probability where we might find an electron
Electrons are constantly moving
Electrons have a specific amount (quantum) of energy, related to their position from the nucleus
1 Angstrom
Red dots represent areas of probability 5
Source:

6. 6
Probability
Suppose you had a new dartboard. What would it look like after you had played darts with it for six months?
Can you predict accurately where the next dart you throw will go?
Can you predict an area where the next dart is likely to go?
Source:

7. Why do we care about what atoms are made of?7
Question
Why do we care about what atoms are made of?

8. Electric Charge
Like charges repel +
Unlike charges attract -
Electric charge is a basic force that causes movement 8

9. Net Charge of an Atom or Ion
The charge on any substance is a result of the total number of
Protons (p) charges, in the nucleus, and
Electrons (e-) - charges, outside the nucleus
If the # of… then the net charge is….
p = e neutral (atom)
p > e positive (ion)
e- > p negative (ion) 9

10. Why are Bonds Formed?
Bonds are formed because of the electrostatic attraction between atoms.
In doing so, the atoms achieve a lower energy state. 10

11. Electrons determine chemical properties of elements
Chemical Bonds are defined as interactions between the valence electrons of different atoms
Electrons move about the nucleus in atomic orbitals called valence shells
Absorption of energy can cause an electron to jump to a higher energy level.
The atom is stable when the outermost energy level of most atoms has eight electrons. (The Octet Rule)

12. Nature always wants to be in the lowest energy state!
Atoms Bond
The outer electrons of both atoms are mutually attracted to the nuclei
Oppositely charged particles form a bond, representing a lower energy state for each of the atoms, releasing energy
Nature always wants to be in the lowest energy state! 12
Source: ibchem.com/IB/ibfiles/ bonding/bon_img/cov3.gif

13. Chemical Bonds and Attractive Forces
Sharing electrons leads to the formation of covalent bonds.
Methane has four covalent bonds between carbon (C) and hydrogen (H). The figure below shows the methane molecule in four different views.

14. Chemical Bonds and Attractive Forces
Sharing electrons leads to the formation of covalent bonds.

15. Chemical Bonds and Attractive Forces
Ions are produced when atoms can obtain a stable number of electrons by giving up or gaining electrons.
For example Na (sodium) can donate an electron to Cl (chlorine) generating Na+ and Cl-. The ion pair is held together by strong electrostatic attractions called ionic bonds

16. Chemical Bonds and Attractive Forces
Sharing electrons is not always equal.
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons

17. Orbital representations of hydrogen and oxygen17
Electron Density is Uneven
Orbital representations of hydrogen and oxygen
The average electron density around the oxygen atom in a water molecule is about 10 times greater than the density around the hydrogen atoms +  – +  – –
A water molecule
This non-uniform distribution of positive and negative charges, called a dipole, leads to the substance’s unusual behavior
Source:

18. Water is a Polar Molecule
More positive ends
The unequal distribution of charges on the water molecule make it a polar molecule
One end is more negative, and one end is more positive
More negative end
A water molecule
- means partial negative charge
+ means partial positive charge 18

19. Hydrogen Bonding Representation
In water, hydrogen bonds form between the partially negatively charged oxygen atom and the partially positively charged hydrogen atom 19
Source: bonddiagram.gif

20. Polar Bonding Hydrogen Bonding

21. Bonding by Analogy:
Dog - Bone Bonds

22. Ionic Bonds: One big greedy thief dog!
Ionic bonding can be best imagined as one big greedy dog steeling the other dog's bone.  If the bone represents the electron that is up for grabs, then when the big dog gains an electron he becomes negatively charged and the little dog who lost the electron becomes positively charged. 

23. Covalent Bonds: Dogs of equal strength.
Covalent bonds can be thought of as two or more dogs with equal attraction to the bones.  Since the dogs (atoms) are identical, then the dogs share the pairs of available bones evenly.  Since one dog does not have more of the bone than the other dog, the charge is evenly distributed among both dogs. The bond is not “polar” because the dogs share equally.

24. Polar Covalent Bonds: Unevenly matched but willing to share.
These bonds can be thought of as two or more dogs that have different desire for bones.  The bigger dog has more strength to possess a larger portion of the bones.  Sharing still takes place but is an uneven sharing.  In the case of the atoms, the electrons spend more time on the end of the molecule near the atom with the greater electronegativity (desire for the electron) making it seem more negative and the other end of the molecule seem more positive.