Chapter 3

Atoms, Elements &

The Periodic Table

Ch 3.1 – Structure of Matter

A. Matter – anything that has mass and takes up space

1. All matter is composed of small particles called atoms

B. Early Ideas about Matter

1. Democritus (460 BC to 370 BC)

a) Greek philosopher who thought the universe was made of empty space and tiny bits of stuff that he called Atomos (atoms)

“Not to be cut”

2. Lavoisier (lived 2000 years after)

a) French chemist proved the

Law of Conservation of Matter

- Matter is not created or destroyed, it only changes form

- Burning wood = ashes left

He showed that the missing mass did not disappear

C. Models of Atoms

1. Models are used for things too small to be seen or too difficult to understand

a) Atom models have been used to explain data gathered by experiments; they are theories

2. Dalton’s Atomic Model

a) Atom’s are too small to be seen by the human eye

b) All matter is made of atoms

c) Each type of matter is made of only one kind of atom

d) Proposed atoms look like tiny spheres

3. JJ Thomson’s Model

a) First to discover atoms are made of smaller parts

b) He discovered the electron using a cathode ray tube experiment

c) Electrons – tiny negatively charged particles (2000 times smaller than protons and neutrons)

d) Proposed atoms looked like a ball (positive) with these small electrons embedded within (negative)

4. Rutherford’s Model

a) Discovered that atoms consisted of lots of empty space in his gold foil experiment

b) Said that the nucleus was made of (+) charged protons and the (–) electrons moved around the nucleus

5. Chadwick’s Model

a) Discovered the neutrally charged neutrons in the nucleus

6. Bohr Model

a) A student of Rutherford’s that proposed the electrons to be orbiting around the nucleus in distinct energy levels which were determined by the amount of energy the electrons had

b) Said electrons orbited

the nucleus like planets

around the Sun

7. Modern Atomic Model (Electron Cloud Model)

a) Electrons move in a cloud around the nucleus not in fixed paths

b) The electron cloud has a radius about 10,000 times greater than the nucleus

8. In recent years protons, neutrons and electrons have been found to be made up of smaller particles called quarks

6 types:

Up Down Strange Charm Top Bottom

Ch 3.2 – The Simplest Matter

A. Elements – matter made of only one kind of atom

1. 115 known elements; 90 naturally occur

2. Synthetic Elements – do not occur naturally; made by particle acceleration in a lab

B. Periodic Table – a chart of the elements that organizes and displays them

1. Has changed over time

2. Modern table credited to Omitri Mendeleev

a) Arranged elements in order of increasing atomic mass (# of protons and neutrons)

b) Had few problems but corrected by rearranging by order of atomic number

(# of protons)

C. Identifying Characteristics

1. Each element is different and has its own unique properties

2. Atomic # - gives the number of protons in the nucleus of the atom

3. Isotopes – elements of the same proton # with a different # of neutrons

ex: Hydrogen has 3 isotopes

1 - 1p+ 0n (Protium)

2 - 1p+ 1n (Deuterium)

3 - 1p+ 2n (Tritium)

4. Mass # - number of protons plus neutrons

5. Atomic Mass – number below element symbol which gives the average of the masses of each isotope of the element

D. Classification of Elements

1. Three categories:

metals, nonmetals, metalloids

a) Metals –

Generally shiny, metallic luster

Good conductors of heat & electricity

All solids at room temp. except mercury

Malleable – can be bent

Ductile – can be drawn into wires

b) Nonmetals –

Dull Appearance

Poor conductors

Many are gases at room temp. (Bromine is liquid)

Solid nonmetals are brittle

97% of your body is made of nonmetals

c) Metalloids - have characteristics of metals and nonmetals

All are solid at room temp.

Some are shiny

Some are conductors

E. Elements in the Periodic Table are arranged in rows and columns

1. Periods/Series – rows that move across; element properties change gradually from left to right

2. Groups/Families – columns that go down the table; each element in a column shares similar properties

a) Representative Elem. – Groups 1-2 & 13-18 Group 1 = Alkali Metals Group 2 = Alkaline Metals Group 7 = Halogens Group 8 = Noble Gases

b) Transition Elements – Groups 3-12 Lanthanide & Actinide Series pulled out across bottom

Interactive Periodic Table

Ch 3.3 – Compounds & Mixtures

A. Substance – matter that has the same composition and properties throughout

B. Compounds – substance whose smallest unit is made up of atoms of more than one element bonded together

1. Have properties that are different from the elements that compose them

C. Compounds have formulas that tell the composition of the compound using the element’s chemical symbol

ex: H2 O = 2 Hydrogen Atoms + 1 Oxygen

D. Mixtures – when 2 or more substances come together but do not combine to make a new substance

1. Can be separated after combining

2. Two types:

a) Homogenous – same throughout; cannot see individual components

b) Heterogenous – not same throughout; can see and separate individual parts