Download Matter

Atomic Structure


Matter is made of tiny particles called atoms.
There are three basic types of particles that
make up an atom:



Protons
Neutrons
Electrons






The dense center of the atom is called
the nucleus.
The particles that are located in the
nucleus are protons and neutrons.
Protons are particles that have a
positive charge.
Neutrons have no charge and are
therefore neutral.
The electrical charge of the nucleus is
positive.
The nucleus contains most of the
atom’s mass.


The negatively charged
particles of an atom
that exist outside the
nucleus are called
electrons.
They travel in an orbit usually close to the
nucleus called an electron cloud.


The structure of the different
types of atoms and how they
are joined together (how
they are bonded to each
other) determine what the
substance is.
Example: graphite, coal and
diamonds are all made of
atoms of carbon.

An element is a substance that is
made of only one type of atom and
cannot be broken down into simpler
substances by normal chemical or
physical means.


The number of protons in an atom will
determine what kind of element it is.
All atoms of the same element
have the same number of protons.
Hydrogen and Helium atoms
Carbon atom
Periodic Table of the Elements



The periodic table is a listing of all the
known elements that exist in the world.
The number of protons in an atom is
equal to the atomic number of the
element. You will find it above the
element’s symbol on the table.
When you look at the table you will
notice that the elements are listed in
order of their atomic number from left to
right.
KEY
Metals
Semimetals
Nonmetals
A neutral atom is one that has an equal
number of protons and electrons.
 The overall charge is therefore neutral.
 In a neutral atom: Atomic number = # of
protons = # of electrons



The atomic mass of an atom is equal to
the number of protons plus the number
of neutrons.
You can determine the number of
neutrons by subtracting the number of
protons from the atomic mass.
Atomic Structure of 14 Elements
Element
Hydrogen
Helium
Oxygen
Carbon
Neon
Nitrogen
Magnesium
Symbol
H
He
O
C
Ne
N
Mg
Atomic
Number
1
2
8
6
10
7
12
Mass
Number
1
4
16
12
20
14
24
Element
Calcium
Iron
Sulfur
Sodium
Chlorine
Potassium
Argon
Symbol
Ca
Fe
S
Na
Cl
K
Ar
Atomic
Number
20
26
16
11
17
19
18
Mass
Number
40
56
32
23
35
39
40
Energy Levels







An energy level represents the area in an atom where an
electron is likely to be found.
Each energy levels can hold only a limited number of
electrons.
The smallest, innermost energy level
can hold only two electrons.
The second energy level can hold up
to eight electrons.
The third energy level can hold up to
8 electrons.
The 4th & 5th can hold up to 18 electrons.
The 6th can hold up to 32 electrons.




Electrons tend to occupy the lowest
available energy level.
The first energy level in an
aluminum atom is filled by two
electrons.
The second energy level is also
filled, by eight electrons.
The third energy level has only three electrons, so it
is not filled.



The number of electrons in the outermost
energy level determines the chemical
behavior of the different elements.
These outermost electrons are called valence
electrons.
Elements with the same number of valence
electrons have similar chemical properties.


For example, a sodium (Na)
atom, with the atomic number
11 and a potassium (K) atom,
with the atomic number 19,
both have just one valence
electron.
Both sodium and potassium are
highly reactive metals, which
means that they combine easily
with other elements.


Elements such as helium (He), neon
(Ne) and argon (Ar) are inert, which
means that they do not easily combine
with other elements.
This is because they have full outermost
energy levels.
Classifying Elements


Each element has a name and a symbol.
The symbol is an abbreviated , or
shortened version, of the element’s name.
Aurum is the Latin
name for gold.

It is used to represent the element in
chemical formulas and equations.



The elements in the Periodic Table are
arranged so that elements with similar
properties are close together.
Example: fluorine (F) and chlorine (Cl) are gases that
react very easily with other elements, so they are
close together in the table.
The Periodic Table gets its name from the fact
that the elements’ properties repeat
themselves every few elements, or
periodically.

The vertical columns of elements are called groups.

Some groups have special names:

Group 1:
The alkali metals

Group 2:
The alkaline earth metals

Group 17:
The halogens

Group 18:
The noble gases – unreactive, so they
almost never react with other elements
to make compounds.
The Periodic Table
Column = Group or
Family
18 columns on the
Periodic Table
Row = Period
7 rows on the
Periodic Table


The horizontal rows of elements are
called periods.
The table also shows which elements
are metals, non-metals, and metalloids.
Metals






All metals look shiny.
Most metals are very hard (a few so soft you can
cut them with a knife).
Metals are also malleable, meaning that they can
be bent, or beaten into different shapes without
breaking.
All metals except mercury are solids at room
temperature because they generally have high
melting and boiling points.
All metals let heat and electricity pass through
them easily, so they are good conductors of heat
and electricity.
Only a few metals are magnetic (ex. - iron).
Nonmetals




At room temperature most nonmetals are
gases, some are solids and one (bromine) is a
liquid.
This is because nonmetals have a wide range
of melting and boiling points.
Nonmetals are not good conductors of
electricity or heat (with the exception of
carbon, which conducts electricity as well as a
metal).
All nonmetals are nonmagnetic.
Metalloids




A few elements, such as silicon, have some of the
properties of metals and some of the properties of
nonmetals.
Since they are not clearly one or the other, they are
called metalloids, or semimetals.
They are used in making semiconductors – materials
which can conduct some electricity better than an
insulator can, but not as well as a metal.
They are used in making electronic components and
microchips.
Compounds



A compound is a substance
that is made up of different
elements.
The atoms of the elements are joined
together by chemical bonds.
Bonds are chemical connections between
atoms.
Types of Bonds

There are two basic types of bonds:




Covalent
Ionic
The reason that bonds occur is that atoms
“want” to have full outer electron shells.
An atom gets a full outer shell by getting
involved in one of the two types of bonds.
Covalent Bonds



Sharing one of more
electrons is one type of
bonding called a covalent
bond.
Example: water is formed
when atoms of hydrogen
share their electrons with
an oxygen atom.
A molecule is the smallest unit of a compound
that has all the properties of the compound.
Ionic Bonds



The second type of bonding is when some atoms
give up electrons, or ionic bonding.
Example: salt is formed
when the sodium gives
up its electron and the
chlorine takes it.
An atom like this that has lost or gained an
electron is called an ion.



We write a + next to the
element’s symbol if its
atom has lost an electron
and a – if it gains an
electron.
For example: Na becomes Na+ because it has more
positive charge than negative and Cl becomes ClOpposites attract! The protons in the nucleus “miss” the
“missing” electron and they stay close to it forming the
bond.



If two types of atoms bond together using
either method, the result is a compound.
In a chemical change, bonds are made or
broken, which leads to a new substance, or
substances being created.
In a physical change, such as making a
mixture or dissolving something, no bonds
are affected.
Mixtures


A mixture is a combination of
things where there are no
chemical changes or bonds.
There are two types of mixtures:
Heterogeneous:





Homogeneous:



Not mixed evenly
Each component retains its own
properties
Examples: pizza, cereal and milk, rocks
in the sand at the beach, banana splits
Mixed evenly throughout
Properties are often different from their
components
Examples: milk, kool-aid, blood, lotion,
window cleaner, glue


A solution is an evenly mixed mixture
(liquid), such as salt water.
Mixtures can be separated by physical
means.

An isotope is an atom that has the same
number of protons as another atom, but
has a different number of neutrons.

Atoms of an element can lose or gain
electrons and still be the same element, but
the atom is no longer neutral. If the number of
electrons is less than the number of protons,
the atom will have a positive charge. Atoms
with more electrons have a negative charge.
Atoms of the same element with a different
number of electrons are called ions.
gases!