CH 7. UNDERSTANDIN

G THE ATOM&

CH 8. ELEMENTS AND CHEMICAL

BONDS

KMS 8th grade science

THE ATOM The smallest piece of an element that

still represents that element.

The atom is made up of main parts

two

Electron Cloud

Nucleus

THE NUCLEUS A small area in the center of an atom

Responsible for most of the atom’s mass Contains positive charge

Contained in the nucleus:protons

neutrons

PROTONS An atomic particle that has a positive

charge Size: Charge: Location: Atomic Mass Unit (amu) =

Larger than electrons

Positive

Nucleus

1 amu

NEUTRONS Neutral particle that exists in the

nucleus of an atom.

Size: Charge: Location: Atomic Mass Unit (amu) =

Larger than electrons (about the same size as a proton)

NeutralNucleus

1 amu

THE ELECTRON CLOUD The area around an atomic nucleus

where an electron is most likely to be located

Contained in the electron cloud:electrons

ELECTRONS A particle with a negative charge.

Size: Charge: Location: Atomic Mass Unit (amu) =

Much smaller than protons and neutrons

Negative

Electron Cloud

1/1,840 amu

CONTRIBUTORS Democritus (pg. 236) Aristotle (pg. 236) John Dalton (pg. 236) J.J. Thomson (pg. 238) Ernest Rutherford (pg. 240) James Chadwick (pg. 245) Niels Bohr (pg. 245)

DEMOCRITUS Proposed that different types of matter

are made from different types of atoms. Proposed that space between atoms

was “empty”

ARISTOTLE 384 – 322 B.C.

Did not believe in Democritus’ idea that between atom’s were empty space

He believed all matter was made of fire, water, air and earth.

JOHN DALTON Late 1700’s All matter is made of atoms that cannot

be created, divided or destroyed. Atoms of the same element have the

same mass and are exactly alike

J.J. THOMSON 1897 Found negatively charged particles

(electrons) and reasoned that they must have a positive charge that balances them out.

ERNEST RUTHERFORD Thomson’s student First atomic model with nucleus Came up with the word proton for

positive charge

JAMES CHADWICK Discovered the neutron Completed the atomic model

NIELS BOHR Proposed that electrons move in circular

orbits, called energy levels, around the nucleus.

ELEMENTS Pure substance made of only one type

of atom A substance made from atoms that all

have the same number of protons.

In the empty box in your notes, look at the periodic table and fill out an elementbox for carbon

CARBON ELEMENT BOX

C

Carbon

12.01

6

Element Atomic Number

Symbol

Atomic Mass

ATOMIC NUMBER The number of protons located in the

atom’s nucleus.

Turn to the periodic table in your text book…can you find the atomic number in the following element boxes?

Oxygen Potassium Gold

PROTONS AND NEUTRONS The number of of the same

element will always be However, atoms of the same element

can have For example: every carbon atom has 6

protons, however some have 6, 7, or 8 neutrons.

protonsthe same

a different number of neutrons

THESE ARE CALLED… Isotopes - atoms of the same element

that have different numbers of neutrons.

Most elements have isotopes.several

MASS NUMBER The sum of protons and neutrons in an

atom.

AVERAGE ATOMIC MASS The average mass of the element’s

isotopes, weighted according to the abundance of each isotope.

The average atomic mass is and based on each isotope’s

Approximately 99% of Earth’s carbon is which is why carbon’s average atomic mass is close to 12 (12.01)

weightedabundance on Earth

Carbon-12

THE ARRANGEMENT OF ELEMENTS Arranged by:

Arranged in order of:

Periodic-

Dmitri Mendeleev (1834-1907)

Increasing atomic mass

Describes something that occurs or repeats in regular intervals.

The three main regions of elements on the periodic table classify elements asMetals, nonmetals, or metalloids

COLUMNS

The (up and down) columns of the periodic table are called

There are groups

Elements in the same group or family have

vertical

groups or families

Similar chemical and physical properties

18

ROWS The horizontal rows of the periodic

table are called Elements in a period

The first element in a period is usually an active , and the last element in a period is always an inactive .

periods

solidgas

are not alike in properties

ROWS Atomic number (number of protons)

Atomic mass (number of protons + neutrons)

Metals are on the

Non-metals are on the

increases from left to right across a period

increases from left to right across a period

left

right

ENERGY LEVELS Different electrons within an atom have

An electron moves around the nucleus at a distance that corresponds to

Electrons to the nucleus have the amount of energy.

Electrons from the nucleus have the energy.

different amounts of energy

the amount of energy it has.closest

least

furthestmost

Electron Energy Levels

ENERGY LEVELS Negatively charged are strongly

attracted to charged nucleus of an atom.

These OUTERMOST electrons can easily be attracted to the nucleus of

We call these OUTERMOST electrons

electrons

positively

other atoms

valence electrons

ENERGY LEVELS Valence Electrons - outermost electron

of an atom that participates in chemical bonding.

These attractions are what cause chemical bonds

HOW TO DETERMINE THE NUMBER OF VALENCE ELECTRONS The number of in each

atom of an element can help determine

The exception to finding number of valence electrons is

valence electrons

the type and the number of bonds it can form

helium

GROUP #/VALENCE ELECTRON Group 1 Group 2 Group 3-12 Group 13 Group 14 Group 15 Group 16 Group 17 Group 18 Helium is the exception and has V.E.

1 valence electron

2 valence electron

valence electrons vary3 valence electrons

4 valence electrons

5 valence electrons

6 valence electrons

7 valence electrons

8 valence electrons

2

**go back to the periodic table in your notes and label the valence electrons.