A ATOMS 1 All matter is made of

A. ATOMS

1. All matter is made of atoms 2. Atomic Parts § Protons-positive (+); some mass; in nucleus § Neutrons-no charge (0); some mass; in nucleus § Electrons-negative (-); no real mass but do take up most of the space around an atom

Atomic Structure

3. Describing Atoms a. Atomic Number = number of protons -In a neutral atom (0 charge), the # of protons = the # of electrons b. Atomic Mass=number of neutrons + Protons

4. Changing Parts a. The number of protons for an atom never changes. BUT-the number of neutrons can change b. Isotopes are atoms of the same element with a different number of neutrons.

Examples of Isotopes

c. Ions • An atom that gains or loses an electron is called an ion – If the atom loses electrons, it becomes positively charged – If an atom gains electrons it becomes negatively charged WHY? -Remember p+ = e- so if we change those numbers, the charge moves in the direction of the larger number of particles. -More on this later when we talk about bonding

ION Example

B. Atomic Theory 1. Early Theory a. Aristotle-all matter flows continuously and is composed of 4 elements -fire, air, earth and water b. Democritus-Disagreed with Aristotle and said that matter was made of small units called “atomos” that were indivisible Aristotle was more popular than Democritus so this theory was ignored for over 2000 years!c

2. Modern Theory a. Dalton (England, 1800’s) atoms. 1. All elements are composed of atoms and they are indestructible-like a solid sphere. They cannot be created or destroyed-LAW OF CONSERVATION OF MATTER 2. Atoms of the same element are exactly alike. 3. Atoms of different elements are different. 4. Compounds are formed by the joining of atoms of two or more elements.

b. Thomson (1897 -England)Discovered negatively charged electrons c. Rutherford(1897 -England)-In 1908, discovered the nucleus.

c. Bohr (1913)-Denmark – said electrons were in orbits or energy levels around the nucleus.

• Energy Levels The energy that an electron has is based on its location around the nucleus. (Electrons that are closer to the nucleus have less energy than those that are farther away from the nucleus)

Energy Levels (cont’d) • • • Level Level 1 -2 electrons 2=8 electrons 3 -8 electrons 4 -18 electrons 5 -32 electrons Each level must be full before another can be started.

EXAMPLE • Nickel has an atomic number of 28 1. 2. 3. 4. Level 1 hold 2 -------28 -2=26 to place Level 2 can hold 8 ----26 -8=18 to place Level 3 can hold 8 ----18 -8=10 to place Level 4 can hold 18 BUT only 10 are left so it will only have 10 in it • We have to show Neutrons (n) and Protons (p+) too. • Protons and electrons are usually equal so we know there 28 protons. – Neutrons are found by subtracting the Atomic number from the atomic mass. Atomic mass 59 - Atomic # 28 =31 neutrons

EXAMPLE It would look like this. . 28 p 31 n

d. Electron Cloud Model • Electrons travel in regions called “electron clouds” • You cannot predict exactly where an electron will be found • Electrons move in