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Atoms, Elements, Compounds

Chapter 7

Structure of the Atom


Atom Structure

Smaller units

Atoms - Basic unit of matter

Retain properties

Building blocks of universe

Various kinds

Over 100 naturally occurring

Periodic table



Different models proposed over last 200 years

Dalton’s Model

Thomson’s Model

Rutherford’s Model

Bohr’s Model

Electron Cloud Model

Inside the Nucleus

1932, James Chadwick


Same mass as proton

No electrical charge

Protons and neutrons

Positively charged

Strong force

Atomic Numbers and Isotopes

Atomic # = Number of protons in the nucleus of an atom

Also represents the # of electrons in the atom

Atom is neutral because + = - charges

Isotopes - atoms of the same element with different numbers of neutrons

Each element has limited # of different isotopes.

C-12 6 n, 6+, 6 e-

C-14 8 n, 6+, 6 e-

Unstable are radioactive isotopes

Mass Number and Atomic Mass

Number of neutrons affect the mass

Total # of p and n = mass number

Number written with a hyphen after the elements name

Carbon – 14, Helium – 3

Helps to distinguish isotopes

Unit used to measure mass

Atomic mass unit


1/12 the mass of a carbon - 12 atom

Measurement is given as an average of the elements isotopes

Check and Explain

1. The # of p and e- of an element

2. Thomson’s – includes electrons

Rutherford’s – includes the nucleus

Bohr’s – levels of energy around nucleus

3. Both the atom’s nucleus and electron cloud contain charged particles. The atomic nucleus is positively charged; the electron cloud is negatively charged. Particles in the electron cloud move around the nucleus

4. O – 16 = 8 p, 8n, 8e-

O – 17 = 8 p, 9n, 8e-

O – 18 = 8 p, 10 n, 8 e-



Elements and Matter

One kind of atom

Can not be broken down by chemical means

Few exist pure in nature

Most combined with other elements

Eg. Na

30 play a role in everyday life

18 do not occur in nature – synthetic

Created in Lab

Properties of Elements





Electrical conductivity

Most solids, some liquids and gases

He, Cu, Fe, Hg, S

Chemical Symbols

Universal Shorthand

All over the world

One or two letters taken from name of element

Sometimes derived from other languages

Au - aurum, Latin for Gold

Check and Explain

An element is made up of only one kind of atom that cannot be changed.

Luster, color, density, texture, electrical conductivity

Made up of one kind of atom, equal number of protons and electrons, single atom has same properties as a large sample of that element.


Defining Compounds

Most elements do not exist alone in nature " free "

Reactive elements

Compound – is a substance made of two or more elements chemically combined

Elements in, on, and around Earth

Living things, rocks, soil

Properties of Compounds

Different from those elements that make it up

Definite composition

Combine in specific combination

CO2, CO, NaCl, CaCO3, C3H8, SiO2

Types of Compounds
Different kinds of atoms
Differ in the way atoms join


Sharing of electrons

Most liquids and gases

CO2, NH4



Charged particle

Combination of + and – ions

Held together by electrical charges

Most are solids

Repeating crystal structure

Usually water soluble

When melted or dissolved conducts electricity

Formulas of Compounds

Combination of symbols and numbers that represent the composition of a compound.

Subscripts – show number of each atom

More than one, written to lower right of symbol

Only one atom, no subscript is written

How do you write a formula for a compound?

Check and Explain

1.Compounds are combinations of the elements on the periodic table. There are more compounds than elements because there are many combinations of those elements.

2. Answers vary

3. Both are combinations of atoms. Ionic compounds are made up of positive and negative ions. Molecular compounds are made up of atoms that share electrons.

4. C12H22O11


Comparing Mixtures and Compounds

Properties of Mixtures

Types of Mixtures

Check and Explain

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