1. 2.4 Chemical reactions and enzymes
The Chemistry of Life
2.1 The Nature of Matter
2.2 Properties of Water
2.3 Carbon Compounds
2.4 Chemical reactions and enzymes

2. Atoms Building blocks of life - the basic unit of matter
Name comes from greek term – atomos – unable to be cut
Very very small – 100million = 1cm
Made of three subatomic particles – protons, neutrons and electrons

3. Subatomic particles Protons and Neutrons - the same mass
Protons have a positive charge
Neutrons carry no charge at all
Strong forces bind protons and neutrons to form a nucleus
Electrons – negatively charged particles
1/1840 mass of a proton
Equal number of protons and electrons = neutral charge

4. Elements

5. Elements Pure substance – consists of only one type of atom
More than 100, but less than 20 are common
Number of protons –atomic number
Atomic number of carbon – 6
Each carbon atom has 6 protons and therefore 6 electrons
Numbers of neutrons in an element can vary

6. Isotopes All carbon isotopes have 6 protons
Number of neutrons can vary
6, 7, 8
There are different isotopes of carbon
Total number of protons and neutrons = mass number
Mass number is used to identify different isotopes
Atomic mass - weighted average of different isotopes

7. Calculating weighted average
Weighed average atomic mass =
sum of (atomic mass X modal abundance) for each isotope of carbon
Because all isotopes have the same number of electrons, all isotopes have the same chemical properties
Mass number
exact weight (amu)
percent abundance 12
98.90 13
1.10
Answer =(12 x ) + ( x 0.011) = amu

8. Radioactive isotopes
When the nuclei of an isotopes is unstable, it is radioactive
This means the nuclei will “break down” at a constant rate over time
Radiation can be dangerous, but also very useful
Can be used to date the age of rock
Can be used to treat cancer
Kill bacteria in food
Use a tracer to follow movements of substances in organisms

9. Chemical compounds
Most elements are found combined with other elements
Chemical compound - combination of two or more elements in definite proportions
We write a chemical formula in a kind of shorthand
Eg. H2O
Water contains one hydrogen and two oxygen atoms

10. Chemical bonds
Electrons in the outer shell dictate what kind of chemical bonds atoms can form
These electrons are called valence electrons

11. Ionic bonds
Where one or more electrons are transferred from one atom to another
This distorts the neutral charge of atoms
Positive and negative ions generated
Positive and negative ions are attracted to each other
A strong bond is formed
Common with extreme ends of the periodic table

12. Salt formation

13. Covalent bonds Sometime electrons can be shared
Moving electrons travel around the nuclei of both atoms
The basis for a covalent bond
Possibility for single, double or triple bonds
Resultant structure called a molecule

14. Van der Waals forces Sharing can sometimes be a bit one sided
Some elements have a stronger ability to attract electrons than others
Even when equal, the rapid movement of electrons can can create regions that have positive and negative charges
Results in a slight attraction between these areas
Not as powerful as ionic bonds!
But can hold molecules together