Atoms and Molecules

Caffeine molecule

Macromolecule –a Protein

Atomic structure• Small, dense nucleus

– Protons: (+) charge– Neutrons : (0) no charge• Electrons (-) found in Electrons (-) found in

orbitals of different energy orbitals of different energy levels around the nucleus.levels around the nucleus.

• # Protons = # electrons• Electrically neutral, as + and

– charges are equal

Energy levels• Electrons fill up

orbitals around the nucleus from the inside out.

• Each level holds only so many electrons

• Level 1- holds 2• Level 2 – holds 8• Level 3- holds 8

Valence electrons•the electrons on the outermost level are called the electrons on the outermost level are called valence valence electronselectrons, and they determine reactivity, and they determine reactivity

•ReactivityReactivity is how likely an atom is to form bonds with is how likely an atom is to form bonds with another elementanother element

Think: How many valence electrons does Ar have? and H?

ElementsElements• Every element has a

unique number of protons.– It is the number of

protons that defines what the element is.

– The atomic number is the number of protons

– The atomic mass is the number of protons plus neutrons

Lithium: Atomic # =

3, Atomic mass = 6

The periodic table• The periodic table is a tool that organizes elements

– Groups (columns). of elements have the same number of valence electrons

– Periods (rows) of elements have the same number of energy levels.

What is a chemical bond?

Attractive forces that hold atoms and ions together, making molecules

• An ionic bond holds ions together

• A covalent bond holds atoms together

Types of bondsTypes of bonds• Covalent bondsCovalent bonds

– Two or more atoms Two or more atoms shareshare electrons.electrons.

– Example: waterExample: water

• Ionic bondsIonic bonds– Formed when electrons are Formed when electrons are

transferred.transferred.– Atoms become charged (ions)Atoms become charged (ions)– Opposite charged Opposite charged ions ions attract attract

each other.each other.– Example: saltExample: salt

Water: two hydrogen atoms plus an oxygen atom.

Salt: one chlorine atom plus one sodium atom.

CompoundsCompounds• Molecules composed Molecules composed

of atoms of two or of atoms of two or more more elementselements..

• Held together by Held together by chemical bonds.chemical bonds.– Chemical bonds require Chemical bonds require

energy to form.energy to form.– Chemical bonds result Chemical bonds result

from outer electrons from outer electrons (valence electrons) (valence electrons) interacting.interacting.

Methane gas molecule CHMethane gas molecule CH44

Think: How many atoms are in methane? How many elements are in methane?

Polarity

• Elections are either shared equally or not between atoms in a compounds

• Polar: When electrons are not shared equally, one end of the molecule is more positive and the other more negative.

• Nonpolar: an even distribution of charge

Summary: answer the following as a 7 sentence paragraph

1. What is the basic structure of an atom?

2. What is an element?

3. Why do elements form bonds?

4. What type of bonds do elements form?

5. What is a compound?

6. What is polarity?