Sucrose is composed of the elements carbon, hydrogen, and oxygen. This is a qualitative expression of composition. A qualitative observation is one that can be made without measurement.

In 100 g of sucrose contains 42.1 g of carbon, 51.4

g of oxygen, and 6.5 g of hydrogen. This is a quantitative expression of composition. A quantitative observation is one that uses measurement. You make quantitative measurements every day when you answer such questions as What’s the temperature? How long was the pass?

A substance is matter with the same fixed composition and properties. A substance can be either an element or a compound. Any sample of pure matter is a substance.

Most of the matter you encounter every day is a mixture. A mixture is a combination of two or more substances in which the basic identity of each substance is not changed. Unlike pure substances, mixtures do not have specific compositions.

Physical properties are characteristics that a sample of matter exhibits without any change in its identity.

Examples of the physical properties of matter include its solubility, melting point, boiling point, color, density, electrical conductivity, and physical state (solid, liquid, or gas).

Chemical properties are those that can be observed only when there is a change in the composition of the substance. Chemical properties describe the ability of a substance to react with other substances or to decompose. Lack of reactivity is also a chemical property.

• The smallest particle of an element that retains the properties of that element.

• Idea of the atom was first suggested

by Democritus

• first subatomic particle discovered

• have a negative charge

• equal to the number of protons and atomic number

• discovered by J. J. Thomson

• found in the electron cloud

• amu 1/1897

• have a positive charge

• equal to the atomic number of the element

• found in the nucleus of the atom

• amu 1

• have a neutral (no) charge

• found in the nucleus of the atom

• approximate amu 1

• center of the atoms

• composed of protons and neutrons

• very dense

• has a positive charge

• discovered by Rutherford in his gold foil experiment.

• atoms that have the same number of protons (thus the same element), but a different number of neutrons.

• alike chemically, but have different masses

• written with the name or symbol of the element followed by the mass number• Carbon-12 or carbon-14

John Dalton (1766-1844) - an English schoolteacher and chemist

The following statements are the main points of Dalton’s atomic theory.

1. All matter is made up of atoms.

2. Atoms are indestructible and cannot be divided into smaller particles. (Atoms are indivisible.)

3. All atoms of one element are exactly alike, but they are different from atoms of other elements.

An atom’s atomic number is the number of protons in its nucleus. The number of electrons in an atom equals the number of protons.

Atoms of the same element always have the same number of protons and electrons but vary in the number of neutrons.

protons = atomic number electrons = protonsneutrons = atomic mass - protons

Atomic Numbe

r

Mass Numbe

r

# of proton

s

# of neutron

s

# of electron

s

Element Name & Symbol

4 9

10 Neon - Ne

23 Sodium – Na

7

9 10

59 Cobalt - Co

Atomic Numbe

r

Mass Numbe

r

# of proton

s

# of neutron

s

# of electron

s

Element Name & Symbol

4 9 4

10 Neon - Ne

23 Sodium – Na

7

9 10

59 Cobalt - Co

Atomic Numbe

r

Mass Numbe

r

# of proton

s

# of neutron

s

# of electron

s

Element Name & Symbol

4 9 4 5

10 Neon - Ne

23 Sodium – Na

7

9 10

59 Cobalt - Co

Atomic Numbe

r

Mass Numbe

r

# of proton

s

# of neutron

s

# of electron

s

Element Name & Symbol

4 9 4 5 4

10 Neon - Ne

23 Sodium – Na

7

9 10

59 Cobalt - Co

Atomic Numbe

r

Mass Numbe

r

# of proton

s

# of neutron

s

# of electron

s

Element Name & Symbol

4 9 4 5 4Beryllium -

Be

10 Neon - Ne

23 Sodium – Na

7

9 10

59 Cobalt - Co

Atomic Numbe

r

Mass Numbe

r

# of proton

s

# of neutron

s

# of electron

s

Element Name & Symbol

4 9 4 5 4Beryllium -

Be

10 Neon - Ne

23 Sodium – Na

7

9 10

59 Cobalt - Co

Atomic Numbe

r

Mass Numbe

r

# of proton

s

# of neutron

s

# of electron

s

Element Name & Symbol

4 9 4 5 4Beryllium -

Be

10 20 10 10 10 Neon - Ne

11 23 11 12 11 Sodium – Na

7 14 7 7 7 Nitrogen - N

9 19 9 10 9 Fluorine - F

27 59 27 32 27 Cobalt - Co

Each energy level can hold a limited number of electrons. The lowest energy level is the smallest and the closest to the nucleus. This first energy level holds a maximum of two electrons. The second energy level is larger because it is farther away from the nucleus. It holds a maximum of eight electrons. The third energy level is larger still and holds a maximum of 18 electrons.

The electrons in the outermost energy level are called valence electrons.

A Lewis dot diagram illustrates valence electrons as dots (or other small symbols) around the chemical symbol of an element. Each dot represents one valence electron.

The maximum number of dots on a the diagram is 8.

The period number tells the number of energy levels of an atom.

Example sodium is in the _____ period, so it must have _____ energy levels.

p+ = ______

n0 = ______

e- = ______

Bohr Diagram

Lewis Structure

Na

_____

Na_____________

_______