7.0 Atoms, elements, ions and compounds

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Atoms, Elements, Compounds

• Atom

• basic building block of all matter

• Element

•Substance that consists of only one type of atom.

•Molecule has two different atoms.

• Compound

• substance that consists of more than one type of

element.

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What is an atom?

Examples of models of atoms:

H

Na

Cl

Hydrogen

atom

Sodium

atom

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Atoms have:

• A nucleus

• small, heavy part of the atom

•An electron cloud

• large, lightweight part of the atom

Nucleus

containing

protons and

neutrons

Electron Cloud

Review

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Atoms and Elements

• 118 known: 90 found in nature, others are man made.

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What is an element?

An element is a substance that

cannot be broken down into

two or more simpler substances

by any chemical means.

- They are arranged in the Periodic Table, classified as metals

and non-metals.

- They may consist of atoms of same element or molecules of

the same element.

Metals (excluding hydrogen) Non-metals (including _hydrogen)

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Examples of elements

Elements are made up of tiny particles

Elements can be further classified into two groups:

Is the smallest particle of an element and has the same chemical properties

of the element

Is made up of two or more atoms that are chemically

bonded together

(note: these atoms are of the SAME element!!)

Hi, I am from the “Noble gas” family

and I work alone

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• a single atom of that element (Ar or H).

• molecules of an element (H

₂

, N

₂

, O

₂

, F

₂

,

Cl

₂

, Br

₂

, I

₂

),

• atoms of elements are present (sodium

found in salt).

How the Term Element is Used

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Examples of molecules

(elements)

H H N N O O O

O O S

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Allotropes of Carbon molecule

(element)

• Carbon is an element but made up of a very large

molecule (also known as MACROMOLECULE)

• There are 3 types of carbon molecular structures

– C

₆₀

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Elements

Elements contain one or more of the same type of atom!

Examples include:

Oxygen – 8 protons per atom

Copper – 29 protons per atom

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Chemistry In Action

Natural abundance of elements in Earth’s crust

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Chemistry In Action

Natural abundance of elements in human body

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• Atoms can form ions by gaining or losing electrons.

 Cations are generally named by using the name of the parent atom.

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Atoms and Ions

• An

ion

is an atom that has become charged by

gaining or losing electrons.

ion cation anion

The sodium atom loses its outermost electron

to form an ion. The sodium ion is stable

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Cation

• A

cation

is a positively charged ion. It is formed when an atom loses

an electron.

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An ion is an atom, or group of atoms, that has a net positive or negative charge.

cation – ion with a positive charge

If a neutral atom loses one or more electrons it becomes a cation.

Na

11 protons

11 electrons

Na+

11 protons

10 electrons

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Anion

• An

anion

is a negatively charged ion. It forms when an atom gains an

electron.

• To name an anion, add –ide to the stem of the element’s name.

• Ex. the anion below is the fluoride ion.

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An ion is an atom, or group of atoms, that has a net positive or negative charge.

anion – ion with a negative charge

If a neutral atom gains one or more electrons it becomes an anion.

Cl

17 protons

17 electrons

Cl-

17 protons

18 electrons

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Calculating Ionic Charge

• Fluorine is one of the most reactive elements

• It will pull an electron off another atom… gaining one extra

negative charge.

• The chemical symbol of the fluoride ion is now F

-

_.

Fluoride Ion

positive charge +9

(protons)

negative charge -10

(electrons) ________

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Ion Charges and the Periodic Table

• The ion that a particular atom will form

can be predicted from the periodic table.

Group or Family

Charge

Alkali Metals (1A)

1+

Alkaline Earth Metals (2A)

2+

Halogens (7A)

1–

Noble Gases (8A)

0

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Isotopes

All atoms of an element have the same atomic

number and the same number of

protons

.

However, atoms do not necessarily have the

same number of

neutrons

.

Mass #

Atomic #

• Nuclear symbol:

• Hyphen notation:

carbon-12

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

12

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Isotopes

+ + + + + + Nucleus Electrons Nucleus Neutron Proton Carbon-12

Neutrons 6 Protons 6 Electrons 6

Nucleus

Electrons

Carbon-14

Neutrons 8 Protons 6 Electrons 6 + + + + + + Nucleus Neutron Proton

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3 p

+

3 n

0 2e

–

_1e

–

3 p

+

4 n

0 2e

–

_1e

–

6 _Li

7 _Li

+ + + Nucleus Electrons Nucleus Neutron Proton Lithium-6

Neutrons 3 Protons 3 Electrons 3 Nucleus Electrons Nucleus Neutron Proton Lithium-7

Neutrons 4 Protons 3 Electrons 3

+ +

+ they have the same number of

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Isotopes

• Chlorine-37

– atomic #:

– mass #:

– # of protons:

– # of electrons:

– # of neutrons:

17

37

17

20

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Cl

37

17

37

17

Cl

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Isotopes of Hydrogen

Hydrogen – 1

Protons = 1 Electrons = 1 Neutrons = 0

Hydrogen – 2

Protons = 1 Electrons = 1 Neutrons = 1

Hydrogen – 3 Protons = 1

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Complete Nuclear Symbols

Isotopes should be written using the complete Standard

notation or by using a

hyphen

symbol. A charge should

be indicated if the atom is not neutral.

EXAMPLE: (hyphen symbol) Chlorine - 37



mass number

Complete nuclear symbol

mass number 37

for an element is

Cl

+2



element symbol and charge

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Practice Problems

1. List out the number of protons, electrons,

and neutrons of

207

Pb

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2. List out the number of protons, electrons,

and neutrons of

55

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3. Atoms of a certain isotope have 73 neutrons and a mass

of 123.

a. What is the atomic number?

b. How many electrons are there?

c. What is the name of the element?

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Compounds

Note that a compound:

• can be broken down into a simpler type of

matter (elements) by chemical means (but not

by physical means),

• has properties that are different from its

component elements, and

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A compound is a substance which is made up of

two or

more elements chemically combined

together.

What is a compound?

- Chemical reactions taking place.

Cu

Qn: Is this a compound?

It only contains one type of element.

Qn: Is this a compound?

H

It only contains one type of element. H O H O O

Qn: Is this a compound?

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So, what is a compound then?

O

H

Water

N

H

Ammonia gas

Consists of two or more elements

And

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Compounds

Microscopic view of

the molecules of the

compound water (gas

phase). Oxygen

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ELEMENTS

COMPOUND hydrogen

(colourless gas) (colourless gas)oxygen

lighted splint heat, light and explosion water (colourless liquid)

Making compounds from their elements

Example: Making water (picture)

Water molecule Oxygen molecule Hydrogen molecule mixture of hydrogen and oxygen water

Example: Making water (models)

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Making compounds from their elements

Example: Making iron sulphide compound

Iron + sulphur  iron sulphide

elements compound

+

yellow _grey



heat

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Heat can be used to break down compounds

into elements or simpler compounds. Such a

chemical reaction is called

thermal

decomposition

.

Compounds can be Decomposed

Mercury(II) oxide

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Compounds contain

more than one

type of

atom!



Carbon Dioxide –

CO

₂

(1 atom of carbon and two atoms of oxygen)

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The Elements

• Just as you had to learn the 26 letters of the

alphabet before you learned to read and write,

you need to learn the names and symbols of

the chemical elements before you can read

and write chemistry.

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Key to reading and writing Chemistry

• Each element has a unique one- or two-letter symbol.

• First letter is always capitalized and the second is not.

• The symbol usually consists of the first one or two letters of the element’s name.

 Examples:

Oxygen O Krypton Kr

• Sometimes the symbol is taken from the element’s original Latin or Greek name.

 Examples:

Gold Au aurum Lead Pb plumbum

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Chemical Symbols

• All

elements

in the

Periodic Table

have symbols

that are

recognized world wide.

• It does not matter which

country

you are in or

the

language

you speak.

• Example: The element

Iron

is always identified

by “

Fe

” and

Oxygen

is “

O

”.

• The names are not always the same but the

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Chemical Symbols

A

Chemical symbol

represents an

element.

Capital letter if only

one letter.

Only first letter

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Sodium

comes from the word sodanum, a

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Chemical Formulas

A

chemical formula

is the combination of

symbols that represent a particular

compound.

The chemical formula indicates which

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Ex. 1: Water molecule

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Ex. 2: Iron Oxide molecule

Fe

₂

O

₃

:

2 atoms of iron for every

3 atom of oxygen

Note: the formula shows the lowest terms.

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Chemical Formulas - Examples

•

Calcium Carbonate (chalk) – CaCO

₃

• Sodium Chloride (salt) – NaCl

• Acetysalicylic acid (aspirin) – C

₉

H

₄

O

₈

• Acetic acid (vinegar) – C

₂

H

₄

O

₂

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Chemical Formulas

• NOTES:

- Each

symbol

in a

formula

represents an

element

.

- If only

one atom

of an element is present in

the compound,

no subscript is used.

- If

more than one atom

of an element is

used, then the symbol is

followed by a

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How to Count Atoms

1 atom of sodium

2 atoms of hydrogen (in a hydrogen molecule)

3 atoms of magnesium 2 atoms of phosphorus

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How do we calculate the number of atoms in a

formula?

Pb(NO

₃

)

₂

Number of nitrogen (N) atoms = 1 x 2 = 2

Number of lead (Pb) atoms = 1

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3 carbon atoms

248 4

2 4 2

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Summarizing

• A compound is made up of

two or more elements

chemically joined together

• A compound has a

fixed composition

• Every compound has a

unique chemical formula

• A compound has a

completely different properties

from its elements

• A

chemical reaction

(decomposition or electrolysis)

is needed

to separate the elements

in the

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Molecules- Elements or compounds?

• A molecule consists of two or more atoms of the

same element, or different elements, that are

chemically bound together.

• It can be a molecule of an element

• E.g. N

₂

, O

₂

, S

₈

• It can be molecule of a compound.

• H

₂

O, CO

₂

, NH

₃

N N

O O

S

O

H

_H

O

C

N

H

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Follow Up Questions

• Use your periodic table to complete the activity on p176 (as a class)