Structure of the Atom

Elements form every object in the world have characteristic properties including: State (solid, liquid, gas) Boiling/melting points Density Solubility

Periodic table: an organized listing of all known elements arranged by increasing atomic number. John Dalton: “father of the atomic theory” Atomic theory: all matter is made up of tiny particles called atoms Matter : anything that has mass and volume. (Mass is determined by–the amount of atoms in it) (Volume means - how much space it covers”.)

tom lehrer's the element song Atom: the smallest particle of an element that still has all the properties of that element.

Parts of an atom 1. nucleus: center part that contains protons & neutrons 2. energy shells/levels: contain the orbiting electrons 3 subatomic particles 1. proton 2. neutron 3. electron

1. proton: positive charge located in nucleus determines identity of element. ALL atoms of an element have the same number of protons. 2. neutron: neutral charge located in nucleus adds mass Isotopes are atoms of the same element with different number of neutrons.

3. electron: negative charge located in energy shell determines physical & chemical properties of element.

READING THE PERIODIC TABLE Atomic number Chemical symbol Atomic mass Atomic mass number : the average mass of the element’s isotopes. Always round to nearest whole number! (Most of the mass of an atom comes from protons & neutrons) Atomic number : equal to the number of protons

Atomic number = number of protons in the nucleus (p + ) It is also equal to the number of electrons (e - ) Carbon (C)– atomic number = 6 protons = 6 electrons = 6 Calcium (C a) – atomic number = 20 protons = 20 electrons =?

Neutrons – To find neutrons, subtract the atomic number from the atomic mass. (Remember to round the atomic mass first.) atomic mass (rounded) - atomic number = number of neutrons. Example: Fluorine = 19 (atomic mass) – 9 (atomic number) = 10 neutrons.

Example: Nickel (Ni): atomic number = 28 protons (p+) = 28 electrons (e-) = 28 atomic mass = 59 neutrons = 59 – 28 = 31

Magnesium (Mg): atomic number = 12 protons (p+) = 12 electrons (e-) = 12 atomic mass = 24 neutrons = 24 – 12 = 12

Bohr’s model: a diagram of an atom showing the location AND the number of protons, neutron, & electrons. The element’s symbol is located below the model. Number of electrons that each shell can hold: 1 st shell – 2 2 nd shell – 8 3 rd shell – 18 4 th shell – 32

P + 36 N 48 Krypton (atomic # 36, atomic mass = 84) Protons = 36 Neutrons = 84 – 36 = 48 Draw nucleus first How to Draw Bohr’s model

Krypton (atomic # 36, atomic mass = 84) Electrons e -= 36 P + 36 N 48 2e - 8e - 18e - 8e - Kr periodic table of rock

Hydrogen (H): atomic number = _______ protons = _______ electrons = _______ atomic mass = _______ neutrons = _______ -- _____ = ______

Draw Bohr’s Model for this element: Calcium atomic number = _______ protons = _______ electrons = _______ atomic mass = _______ neutrons = _______ -- _____ = ______

Group or family: the elements in a column There are 18 groups or families and these elements have similar properties. Period: the elements in a row There are 7 periods and they increase from left to right in valence electrons.

Predicting reactions between element METALS react with NONMETALS to form ionic compounds. Elements to the left of stair stepped line are metals (except H) Elements to the right of stair stepped line are non- metals (except H) Elements along the line are metalloids (except Al which is a metal).

Predicting Reactions between Elements to form ionic compounds. Metals react with non-metals to form ionic compounds. Will Na react with Br? _____ Will Ca react with Ag _____ Will S react with Cl? _______

Most reactive metals are in Group 1 In metals, reactivity increases from top to bottom. Francium is the most reactive Most reactive non-metals are in Group 17 In non-metals, reactivity decreases from top to bottom. Fluorine is the most reactive

NOBLE GASES The elements in group 18 are called Noble Gases. They are said to be “ inert” which means that they don’t readily react with other elements.