1. Biochemistry
Nature of Matter

2. All matter is made of elements and compounds
The Nature of Matter
All matter is made of elements and compounds
Elements are substances that cannot ordinarily be broken down into simpler substances
Oxygen: O
Calcium: Ca
Compounds are combinations of different kinds of elements
Water: H2O
Sodium Chloride: NaCl
Even though this class is biology, we have to talk about chemistry, so we will begin with a review of the nature of matter. All matter, including the matter living things are made of, is made of elements and compounds. Remember that elements are substances that cannot ordinarily be broken down into simpler substances – things like hydrogen, oxygen, and carbon. Compounds are combinations of different kinds of elements – things like water and carbon dioxide.

3. Elements & Atoms Elements are all made of one kind of atom
Carbon and oxygen are elements
Atoms are composed of 3 kinds of particles:
Protons, positive charge, in nucleus
Neutrons, no charge, in nucleus
Electrons, negative charge, surrounding nucleus
Elements are all made of one kind of atom. This means that all the atoms that make up a sample of carbon are carbon atoms. All the atoms that make up a sample of oxygen are oxygen atoms. Carbon and oxygen are elements. Remember that all atoms are composed of 3 kinds of particles. Protons have a positive charge, a mass of 1 atomic mass unit, and are found in the nucleus of the atom. Neutrons have no charge (they are neutral), also have a mass of 1 atomic mass unit, and are also found in the nucleus of the atom. Electrons have a negative charge and are found surrounding the nucleus.

4. Atomic Number & Mass
The number of protons an atom has is its atomic number
The total number of protons and neutrons is the atomic mass
Electrons are not considered to have mass because they are so small
The number of protons an atoms has is its atomic number. Carbon has an atomic number of 6, which means that all carbon atoms have 6 protons. If they had 5 or 7, they would be different elements. The total number of protons and neutrons is the atomic mass of the atom. Since each proton and neutron has a mass of 1 atomic mass unit, then adding them all up gives you the mass of the atom. Electrons are not considered to have mass because they are so small. Actually, an electron has a mass of about 1/1800 of an atomic mass unit. Since atoms are so very small, you can see why electrons are said to have no mass.

5. Isotopes
Atoms of the same element can have different numbers of neutrons
Atoms of the same element with different numbers of neutrons are called isotopes
Atoms of the same element can have different numbers of neutrons. These atoms with different numbers of neutrons are called isotopes. Since they all still have the same number of protons, they are atoms of the same element. The differing numbers of neutrons gives each of them a different mass.

6. Isotopes of Carbon Nonradioactive carbon-12 Nonradioactive carbon-13
6 electrons
6 protons
6 neutrons
8 neutrons
7 neutrons
Here are 3 common isotopes of carbon. Fill in the numbers of protons, electrons, and neutrons on the chart on your notes. Most carbon atoms are carbon-12, meaning they have an atomic mass of 12 (6 electrons and 6 protons plus 6 neutrons). Some carbon atoms are carbon-13 – they have 6 protons and 6 electrons, but 7 neutrons. The only difference between a carbon-12 atom and a carbon-13 atom is that one neutron. The atoms still form compounds the same way – one is just a tiny bit heavier than the other. Note the diagram calls each one “nonradioactive.” This means they are each stable elements and do not decay into simpler substances and give off radiation. The third common kind of carbon atom is carbon-14. This one had 6 protons, 6 electrons, and 8 neutrons. Notice this one is called “radioactive.” That means that this kind of carbon atom is unstable, and over time will decay or change into other, more stable, atoms. You may have heard of carbon-14, which is commonly used to figure out how old certain kinds of fossils and ancient artifacts are.

7. Chemical Compounds
In nature, most elements are combined with other elements to make compounds
A compound is composed of atoms of 2 or more different elements in a definite proportion or ratio
Carbon dioxide (CO2) is a compound of carbon and oxygen
In nature, most elements are combined with other elements to make compounds. A compound is composed of atoms of 2 or more different elements in a definite proportion or ratio. Carbon dioxide is a compound of carbon and oxygen. You can tell from the formula, CO2, that each molecule of carbon dioxide has 1 atom of carbon and 2 atoms of oxygen. Remember, the symbol for the element stands for the 1st atom of that type in a compound, and the subscript, or small number at the bottom right, tells you how many atoms there are if there are more than one.

8. Chemical Bonds Chemical bonds form between atoms in a compound
There are 2 kinds of bonds:
Ionic bonds form between atoms that either give up or receive electrons
Covalent bonds form between atoms that share electrons
When atoms combine to form compounds, chemical bonds form between the atoms in the compound. There are 2 kinds of bonds. Ionic bonds form between atoms that either give up or receive electrons. Covalent bonds form between atoms that share electrons.
Covalent Bond

9. When atoms give up or accept electrons, they become ions
Ions and Molecules
When atoms give up or accept electrons, they become ions
Ions are charged particles
Ions can be either negatively or positively charged
Ionic compounds form when negative & positive ions are electrically attracted to each other
Ionic compounds are neutral in charge
Remember, when atoms give up or accept electrons, they become ions. Ions are charged particles and can be either negatively or positively charged. If an atom loses electrons, which have a negative charge, the atom that is left will have more protons than electrons and will be positively charged. If the atom gains electrons, then it will have more electrons than protons so it will be negatively charged. Ionic compounds form when negative and positive ions are electrically attracted to each other. Remember, opposite charges attract each other and like charges repel. When the ionic compound forms, the number of positive charges balances the number of negative charges, adding up to zero. This makes ionic compounds neutral in charge.

10. Ions and Molecules
When atoms share electrons, they form covalent bonds
A covalent bond is one shared pair of electrons
Atoms in covalent compounds can share 1, 2, or 3 pairs of electrons
The smallest particle of a covalent compound is called a molecule
When atoms share electrons, they form covalent bonds. A covalent bond is one shared pair of electrons. This means that two electrons orbit around both atomic nuclei, spending a relatively equal amount of time around each nucleus and making each atom think it has both of them. Atoms in covalent compounds can share 1, 2, or 3 pairs of electrons (this means 2, 4, or 6 total electrons), forming single, double, or triple bonds between the atoms. Also remember that the smallest particle of a covalent compound is called a molecule.

11. Van der Waals Forces
Some atoms in a covalent molecule have a stronger attraction for electrons than other atoms do
If electrons spend more time near one part of a molecule than another, the molecule can have oppositely charged regions
If molecules have charged regions, those regions will have attractions for oppositely charged regions of other molecules
These forces can hold molecules of a substance together
Even though the shared electrons spend relatively equal amounts of time around each nucleus, some atoms in a covalent molecule can have a stronger attraction for electrons than other atoms do. For instance, an oxygen atom has an atomic mass of 16, compared to the atomic mass of a hydrogen atom, which is 1. Since the oxygen nucleus has 8 protons, and therefore 8 positive charges, it has a stronger attraction for the electrons than the puny 1 proton of a hydrogen atom. The electrons shared by oxygen and hydrogen in a water molecule are therefore going to spend slightly more time near the oxygen nucleus than near the hydrogen nucleus. If electrons spend more time near one part of a molecule than another, the molecule can have oppositely charged regions. If molecules have charged regions, then those regions will have attractions for oppositely charged regions of other molecules. These forces can hold molecules of a substance together. That’s why water droplets bead up on a waxy surface rather than separate – the attractive forces called van der Waals forces hold the water molecules together.