Elements, Atoms, Ions
The Elements
What elements do you
think are most
abundant in human
body?
Oxygen
Carbon
Hydrogen
Nitrogen
Calcium
Phosphorus
Magnesium
Do you know chemical formulas for any
compounds? H 0
2
CO2
NaCl
???
What do you know about
the atom?
What are electrons?
What are protons?
What are neutrons?
The Periodic Table

What does “Periodic” mean

What does the periodic table tell us?
Name an element that is
normally a liquid, one that is
normally a solid and one
that is normally a gas
Liquid: Mercury, Bromine
Solid: Sulfur, Carbon, Iron, Copper ….
Gas: Oxygen, Nitrogen, Hydrogen, Helium …
Elements

Earth – about 88 elements occur naturally

These elements combine to form all of the compounds on our planet

Known elements (including man-made) number around 115 (scientists
always working on producing more)

Chemists use standard names and symbols for elements. You will need to
learn to write and recognize the most common.
You will be responsible for knowing names
and symbols of the following:
Oxygen (O)
Silicon (Si)
Aluminum (Al)
Iron (Fe)
Lithium (Li)
Hydrogen (H)
Calcium (Ca)
Carbon (C)
Sodium (Na)
Boron (B)
Potassium (K)
Magnesium (Mg) Nitrogen (N)
Sulfur (S)
Bromine (Br)
Chlorine (Cl)
Phosphorus (P)
Manganese (Mn) Barium (Ba)
Platinum (Pt)
Fluorine (F)
Gold (Au)
Silver (Ag)
Zinc (Zn)
Lead (Pb)
Iodine (I)
Helium (He)
Neon (Ne)
Copper (Cu)
Mercury (Hg)
What do we mean by “Element”?

Microscopic form – single atom of an element, e.g. H, C, F, W

Microscopic form – molecule made up of atoms of one element (H2, O2, S8)

Macroscopic form - Sample of element large enough to weigh

Generic form – referring to the atoms of element in various forms and
combinations (e.g. the human body contains a lot of the element Oxygen)
John Dalton – early 1800s
Dalton’s Atomic Theory

Elements are made of tiny particles called atoms

All atoms of a given element are identical

The atoms of a given element are different form those of any other element

Atoms of one element can combine with atoms of other elements to form
compounds. A given compound always has the same relative numbers and
types of atoms

Atoms are indivisible in chemical processes. They are not created or destroyed in
a chemical process. A chemical reaction simply changes the way atoms are
grouped together.
Law of Constant Composition


A given compound always contains the same proportions of the elements. It
doesn’t matter where the sample of the compound comes from.

Water always contains 8g of Oxygen for every 1g of Hydrogen

Carbon Dioxide always contains 2.7g for every 1g of Carbon
Dalton’s atomic theory helped explain the law of constant composition

A pair of elements could combine in more than one way

NO

NO2

N2 O
Formulas of Compound

A compound is substance that is composed of the atoms or two or more
elements.

A compound always contains same relative numbers of atoms of each
element (e.g. water always has 2 hydrogens and 1 oxygen)

Chemical formulas – atoms are indicated by the element symbols; number
of each atom is indicated by a subscript – a number that appears to the right
of and below the symbol for the element

NH3
H2O2
CH4
C6H12O6

When only one element in the compound, you don’t write the 1 as a subscript
Try to write some chemical formulas
A compound with 2 Nitrogens
and 5 Oxygens
 N2O5
A compound with 3 Carbons
and 8 Hydrogens
•C3H8
Write the chemical formula for the
following compounds:

A molecule that contains four phosphorous atoms and ten oxygen atoms
P4O10

A molecule that contains one uranium atom and six fluorine atoms
UF6

A compound that contains one aluminum atom for every three chlorine
atoms
AlCl3