Chemistry

A walk down memory lane…

Or at least it should be

If you can cook, you can do chemistry!

•The ingredients = reactants

•The cake/ cookies = product

•You only get out what you put in (Conservation of mass)

•Your products do not have the same properties as the reactants

•Does a cake taste the same as raw eggs, flour, etc?

Atoms – The smallest unit of matter that cannot be broken down by

chemical means*All matter consists of atoms

Nucleus

•Protons (+)

•Neutrons (0)

Electron Cloud

•Electrons (-)

* Nuclei can only be changed by fission or fusion! *

Electron Clouds

• Areas of probability• Electrons do not really

travel in orbits like planets– Bohr Model

• Electrons are in clouds• The farther from the

nucleus, the easier an e- is lost

S orbital

p orbitals

Elements: a pure substance made of only one kind of atom

•Each element:

• Has a different number of protons

•Has a symbol (one or two letters)

•Organized on the periodic table

36

Kr

Krypton

83.80

Symbol

Atomic Number

Atomic Weight

How do we figure out the number of protons, neutrons, and electrons?

• Atomic Number = the number of protons which = the number of electrons

• Atomic Weight = the total mass of the atom. Comes from the combination of protons and neutrons

36

Kr

Krypton

83.80

Protons = atomic number = 36

Electrons = atomic number = 36

Neutrons = atomic weight – atomic number = 84-36= 48

Isotopes: atoms of the same element that have the same number of protons, but a

different number of neutrons

• Some isotopes are stable

• Some break apart and release energy (fission)

This is the reason why atomic weights are NOT whole numbers!

•Organized by properties: Periodicity

•Period – horizontal rows

•Group – Vertical column

•Valence electrons – outermost e-, involved in bonding, same as the group number for the main block elements

Patterns in the Periodic Table

• Diameter decreases as you move along the row from left to right

• Diameter increases as you move down the column

• Each column reacts similarly, because they have the same number of valence electrons

• Metals are on the left and nonmetals on the right

Lets put some atoms together!

• Compound – two or more atoms joined together

• Molecule – two or more atoms share electrons

Types of Chemical Bonds• Ionic

– Electrons are transferred– Makes ions when dissolved – Forms between a metal and a nonmetal

• Covalent– Electrons are shared– Forms between 2 nonmetals– Polar: e- are NOT equally shared– Non-polar: e- ARE equally shared* Don’t forget: “Like dissolves like”

Metallic Bonds

• Electrons move from one atom to the next

• Forms between 2 metals

Hydrogen Bond

• Between 2 polar MOLECULES

• Weak bond• Positive and negative

charges attract much like opposite poles of a magnet

Partially Negative

Partially Positive

*This allows for adhesion, cohesion, and capillary action in water*

Balancing Chemical Formulas

• Step 1: determine the charge of the ion each element will form

• Step 2: Write the metal first, the nonmetal second

• Step 3: the charge of one atom is the subscript of the other

Mg2+ Cl-

MgCl2

Polyatomic Ions

• “ion with many atoms”• The atoms in the polyatomic react as if they are

one atom – they do not rearrange• Written with parentheses around them if more

than one polyatomic is in the compound

• Mg(OH)2