1. Atoms Once believed to be the smallest particles that made up matter
Nucleus: Protons and Neutrons. ~same mass
Protons and neutrons are made of quarks.
Electron Cloud: Electrons. Much smaller mass than protons and neutrons.
Protons are positively charged
Neutrons have no charge
Electrons are negatively charged
Atoms are neutral since they have the same number of protons and electrons.

2. Atomic Structure The nucleus is located in the center of the atom.
The electron cloud which surrounds the nucleus contains electrons spinning around the nucleus.

3. Current Atomic Model
The smallest particles of matter are now believed to be the quark and the electron.
Protons and Neutrons are made from quarks.

4. Electron Arrangements
The electrons are arranged in energy levels within the electron cloud.
Each energy level or shell is labeled with a number or letter. For example K-Shell or energy level 1
Each energy level or shell can hold a maximum number of electrons: #e- = 2n2 where n = energy level. Level 1 holds 2 electrons.
Electrons closer to the nucleus have the lowest kinetic energy because of attractive forces between the electrons and protons.

5. Atomic Structure Diagrams
Elements are made up of atoms with a specific atomic number (number of protons)
For example, all Helium elements contain 2 protons (atomic number 2).
Atomic structure diagrams show how the electrons are arranged in the different energy levels or shells within the electron cloud.

6. Atomic Structure Diagram
P= protons, N= neutrons found in nucleus.
How many protons should this atom have?
If its mass number is 23, how many neutrons should it have? P N E

7. Properties of Atoms
Atomic radius – the distance from the nucleus to the outer edge of the electron cloud.
Ionization energy - The energy required to remove the outermost (highest energy) electron from a neutral atom in its ground state in order to form a cation.
Electron affinity - The energy given off when a neutral atom in the gas phase gains an extra electron to form a negatively charged ion.
Electronegativity - a measure of the attraction of an atom for the electrons in a chemical bond.

8. Ions If an atom gains or loses electrons, it forms an ion.
Cations – positively charged due to loss of electrons.
Anions – negatively charged due to gain of electrons.

9. Isotopes
An atom’s mass number is the total number of protons and neutrons.
When like atoms of the same element have different number of neutrons, they are called isotopes.
Isotopes of one element all have the same number of protons (atomic number, Z) but different numbers of neutrons (thus different atomic weights, A).
Every element has several isotopes

10. Science Changes Over Time
How did the following theories change
Democritus thought that atoms were the smallest particles that make up matter.
Dalton thought that atoms could not be created, divided, or destroyed.
Dalton thought that all atoms of the same element were exactly alike.
Scientists accepted that protons, neutrons, and electrons were the smallest subatomic particles.