1. Elements, Compounds, and Mixtures

2. Elements Made up of only one type of atom
Can exist as a single atom or as a molecule
Molecule: two or more atoms held together by a chemical bond
Examples: He, O2, N2

3. Atoms Each element has a specific atom An atom has 3 main parts:
Protons: positively charged part of an atom. Has a mass of 1 amu (atomic mass unit)
Neutrons: part of an atom with no charge. Has a mass of 1 amu.
Electrons: negatively charged part of an atom. Mass is too small to measure (~0 amu)
Protons and neutrons are in the nucleus.
Electrons rapidly orbit the nucleus in layers called energy levels

4. Compounds
When atoms of different elements join together by chemical bonds
Always exist as molecules (in same ratio)
Properties are different from the component elements
Examples: H2O, CO2, C6H12O6

5. Mixtures When more than one substance are mixed together.
Can be made from elements &/or compounds
The substances do not join chemically and keep their own properties
Substances can be separated out of mixture.
Ex: bag of skittles, air

6. Periodic Table A chart organizing information about all known elements
Periods- the rows of the periodic table
Corresponds to electron energy levels
Groups- the columns of the periodic table
Atoms in the same group have the same set up of their outer (valence) electrons
Elements in the same group behave similarly

7. Atomic Arrangement- nucleus
Protons and neutrons are located in the nucleus
# protons = atomic number (defines the element)
# neutrons = atomic mass – atomic number
Round to the whole # for atomic mass. The number is a decimal because it’s an average.
Isotope- atoms with the same number of protons, but different number of neutrons.

8. Atomic arrangement- energy levels
Electrons are found orbiting the nucleus in a path called an orbital, in layers called energy levels.
The number of electrons is equal to the number of protons.
Elements in the first period of the PT have 1 layer of electrons.
This layer can hold up to 2 electrons.

9. Energy levels continued
Elements in the second period of the PT have 2 layers of electrons.
This 2nd layer can hold up to 8 electrons.

10. Energy Levels continued
Elements in the third period of the PT have 3 layers of electrons.
This 3rd layer can hold up to 8 electrons.

11. Valence electrons
Electrons in the outer layer or shell are called valence electrons.
Atoms want to gain or lose electrons in order to have a full outer layer.
When an atom gains or loses an electron, the charged atom is called an ion.
Anion: An atom that has gained an electron and has a negative charge (-ide)
Cation: An atom that has lost an electron and has a positive charge

12. Bonding
Atoms form bonds to complete their outer layer of electrons and become neutral.
Ionic bond: when oppositely charged ions attract forming an ionic compound
Covalent bond: when atoms share one or more PAIRS of electrons (give one, get one).
This happens when both atoms have almost full outer shells.