ATOMS– THE BASICSAtoms:• Building blocks of all things• Smallest particle that can still be

considered an element

Structure:

Particle Charge Mass Where found

Proton +1 1 amu Nucleus

Neutron Neutral, no charge

1 amu Nucleus

Electron -1 0.00056 amu

Electron cloud

ATOMS– THE BASICS

Atomic Number and

Number of protons, number of electrons

Element symbol

Average atomic mass of element

***Atomic mass = Protons + Neutrons

The number of protons will always equal the number of electrons giving an overall neutral charge for the atom unless indicated.

ATOMS– THE BASICS

Neils Bohr– believed that electrons orbit the nucleus

-first energy level can hold two electrons

-every other energy level can hold 8 electrons

Rules for drawing structures

1.) Electrons can only be placed at 12, 3, 6 and 9 position, like a clock

2.) when drawing, put electrons by themselves first then pair up

Lets look at carbon**The electrons on the

outer most shell are

called valence electrons

--these have the highest energy

and are involved in bonding

ATOMS– THE BASICSGilbert Newton Lewis– Lewis dot structures for valence electrons

**Lewis dot structures are also known as electron dot diagrams

CElectron Dot DiagramsThe valence electrons of an atom are shown as dots around the symbol of the element.

ATOMS-THE BASICSTHE PERIODIC TABLE

Elements are arranged by atomic number Columns = groups or families

Families have similar properties Rows = periods

Number or valence electrons can be

determined by looking at group number Reactivity decreases from left to right

You should be able to locate the following Alkali metals-highly reactive with water Alkaline Earth Metals Carbon Family Halogens-react easily with other elements Noble gases

B, Si, Ge, As, Sb, Te, At = Metalloids-lose or share

electrons Metalloids = some properties of metals and some properties

of non metals, can conduct electricity under some conditions

(determined by temp. and exposure to light) often used as computer

chips, lasers and solar cells

To the left of above elements = Metals, lose valence electrons Metals good conductors of electricity and heat, shiny and malleable and

ductile

To the right of the above elements = Non metals, gain or share electrons Non metals = poor conductors, if solid-dull and brittle, many are gases at room temp.

ATOMS-THE BASICSIONIC BONDING

Ion- atom or group of atoms with a charge

Ionic Bonding occurs between non metals and metals which are oppositely charged to form ionic compounds which are neutral

Electrons are transferred, given away by one and taken by the other

Number of electrons that are transferred is

determined by number of electrons in valence shell

Remember—we want full, stable, happy shells!

Every valence electron wants to have a partner

Metals Non Metals

Lose electrons Gain electrons

Positive charge Negative charge

Cation Anion

ATOMS-THE BASICSIONIC BONDING

Formulas and Names of ionic compounds positive ion (metal) first followed by negative ion (non metal) Add subscripts if needed to balance the charges

Subscripts tell us the number of that particular atom in the

compound, if only one atom, no subscript is written

Naming Ionic Compounds Positive ion is usually the name of the metal If negative ion is a single element, name ends in ide

LiF = Lithium Fluoride

If negative ion is a polyatomic ion, name ends in ate CaCO3 = Calcium Carbonate

Coral Reefs

Corals make calcium carbonate, which helps protect them.

When coral dies, its calcium carbonate shell remains and adds structure to the reef.

Which part of the formula represents the carbonate ion?

What is the charge of each ion in the compound?

Lets look at a couple of examples: Potassium and Fluorine

Calcium and Chlorine

LETS REVIEW IONIC BONDING What is an ionic bond? Atoms will transfer one or more ___________________ to another to

form the bond. Each atom is left with a ___________________ outer shell. An ionic bond forms between a ___________________ ion with a

positive charge and a ___________________ ion with a negative charge.

Example B1: Sodium + Chlorine Example B2: Magnesium + Iodine Example B3: Potassium + Iodine Example B4: Sodium + Oxygen

HaliteIons in ionic compounds are arranged in three-dimensional shapes called crystals. Some have a cubic shape.

GalenaGalena, or lead sulfide (PbS), has a structure similar to that of table salt.

ATOMS-THE BASICSCOVALENT BONDING

Covalent bonding occurs between two non metals Electrons are SHARED The bonded atoms form a molecule

Molecule-neutral group of atoms joined by a covalent bond

The bond that forms can be: Single bond-one

pair of electrons shared Double bond-two

pairs of electrons shared Triple bond-three pairs of

electrons shared

Lets look at some examples Hydrogen and oxygen Oxygen Nitrogen

Sharing ElectronsBy sharing 2 electrons in a covalent bond, each fluorine atom gains a stable set of 8 valence electrons. Which are the shared electrons that form a covalent bond between the 2 fluorine atoms?

ATOMS-THE BASICSCOVALENT BONDING

First atom, just its name, unless there are multiple of that atom Second atom, add prefix to indicate how many, then “ide” on end 1- mono

2- di3- tri4- tetra5- penta6- hexa7- hepta8- octa9- nona10- deca

Name the elements in the same left-to-right order that they have on the periodic table, except that you would have to squeeze hydrogen in between nitrogen and oxygen.  

Example: CO = Carbon monoxide

N2S3 = Dinitrogen TriSulfide

POLAR VS. NON POLAR COVALENT BONDS

Although electrons are shared, they are not always shared equally

Sharing is determined by electronegativity

measure of the attraction of an atom for the

electrons in a bond Higher electronegativity-greater the attraction for

electrons Electronegativity increases as you go

from left to right and bottom to top

Non polar bond- equal sharing Polar bond- unequal sharing, causes atoms to

have slight charge

First check symmetry, then check electronegativity Symmetrical = could be non polar, then check electronegativity Non symmetrical = probably polar

Nonpolar and Polar Bonds Hydrogen forms a nonpolar bond with another hydrogen atom. In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does. The bond formed is polar.

ELECTRONEGATIVITY Electronegativity can be understood as chemical property describing an atom's ability to attract and bind to

electrons. Because electronegativity is a qualitative property, there is not a standardized method for calculating electronegativity. However, the scale that most chemists use in quantifying electronegativity is the Pauling Scale, named after the chemist Linus Pauling. The numbers assigned by the Pauling scale are dimensionless due to electronegativity being largely qualitative. Electronegativity values for each element can be found on certain periodic tables. An example is provided below.

FORCES BETWEEN POLAR MOLECULES Polar molecules are attracted to one and other

due to their slight charges

The forces that hold these molecules together are called van der Waals forces

van der Waals forces also pull molecules to each other Read page 118 van der Waals forces cause a geckos feet to

grip smooth surfaces such as glass

LETS REVIEW COVALENT BONDING What is a covalent bond?

Atoms ___________________ one or more electrons with each other to form the bond.

Each atom is left with a ___________________ outer shell. A covalent bond forms between two ___________________.

Example C1: Hydrogen + Chlorine Example C2: 2 Hydrogen + Oxygen Example C3: Chlorine + Chlorine Example C4: Oxygen + Oxygen

PROPERTIES OF IONIC AND COVALENT COMPOUNDS/MOLECULES

Ionic Compounds Covalent Molecules

Dissolve easily in water Do not dissolve easily in water

When dissolved in water, conduct electricity

Do not conduct electricity--Why? No charged particles

Hard brittle crystalsCrystals-orderly, 3D

structure

“Soft”, irregular structure

High melting points --NaCl (table salt) melts at

801oC

Low melting and boiling points

--C12H22O11 (table sugar) melts at 109oC