Elements, Atoms & Ions
Chapter 4
Copyright©2004 by Houghton Mifflin Company.
All rights reserved.
1
4.1 Elements

Over 112 known, of which 88 are found in nature



others are man-made
Man-made elements are unstable
Abundance is the percentage found in nature


oxygen most abundant element (by mass) on earth
and in the human body
the abundance and form of an element varies in
different parts of the environment
2
4.2 Elemental Symbols




Each element has a unique symbol used to
abbreviates its name
The symbol of an element is 1 or 2 letters from
it’s name
If two letters, the second is lower case
Fluorine F
Zinc
Zn
Gold - aurum
Au
Oxygen O
Chlorine
Cl
Lead - plumbum
Pb
Neon
Ne
Cadmium
Cd
Sodium - natrium
Na
Silicon
Si
Platinum
Pt
Iron - ferrum
Fe
You must learn all 44 of the symbols and element
names given in Table 4.3
3
4.3 Dalton’s Atomic Theory

Elements are composed of atoms

All atoms of a given element are identical


all carbon atoms have the same chemical and
physical properties as other carbon atoms
Atoms of a given element are different from
those of any other element

carbon atoms have different chemical and
physical properties than sulfur atoms
4
4.3 Dalton’s Atomic Theory

Atoms of one element combine with atoms of
other elements to form compounds.

Law of Constant Composition
 all samples of a compound contain the same
relative numbers and types of atoms - the
same chemical formula
5
4.3 Dalton’s Atomic Theory

Atoms are indivisible in a chemical process.



All atoms present at the beginning of a reaction
are present at the end
Atoms are not created or destroyed, just
rearranged
Atoms of one element cannot change into atoms
of another element

cannot turn lead into gold by a chemical reaction
(alchemy is a nuclear process)
6
4.4 Formulas of Compounds

Each atom present in a compound is
represented by its elemental symbol

The relative number of each type of atom is
indicated with a subscript written to the right
of the symbol

When only 1 atom of an element is present in
the compound, the subscript is not written
H 2O
CO
H 2O2
CO2
O2
7
4.5 Structure of the Atom
Electrons
 Tiny, negatively charged particle
 Very light compared to mass of atom


1/1836th the mass of a H atom
Move very rapidly within the atom
8
4.5 Structure of the Atom
The Nucleus
 The nucleus is the tiny dense center of an atom


Most of the atomic mass is due to the nucleus



the volume is about 1/10 trillionth the volume of
the atom
The nucleus is positively charged
the amount of positive charge of the nucleus
balances the negative charge of the electrons
The electrons move around in the empty space
of the atom surrounding the nucleus
9
4.5 Structure of the Atom
Protons

One type of particle in a nucleus is a proton



charge = +1
mass is about the same as a hydrogen atom
A neutral atom has equal numbers of protons and
electrons
Neutrons

Another nuclear particle is a neutron


has no charge
has a mass very slightly more than a proton
10
4.6 The Modern Atom

We know atoms are composed of three main
pieces - protons, neutrons and electrons

The nucleus contains protons and neutrons

The nucleus is only about 10-13 cm in diameter

The electrons move outside the nucleus with an
average distance of about 10-8 cm


therefore the radius of the atom is about 105 times
larger than the radius of the nucleus
An atom is mostly empty space
11
4.7 Isotopes

All atoms of a given element have the same number
of protons, but can have varying numbers of
neutrons

Atomic number, Z is the number of protons in an
atom

found on the Periodic Table
12
4.7 Isotopes

Atoms of an element with different numbers of
neutrons are called isotopes

All isotopes of an element are chemically identical
 undergo the exact same chemical reactions
because they have the same number of protons

Different isotopes of an element have different
masses
 Different number of neutrons

Isotopes are identified by their mass numbers, A
 mass number = protons + neutrons
13
4.7 Isotopes

Different numbers of protons indicate different
elements

Different number of neutrons indicate different
isotopes of an element

Different number of electrons give ions, charged
atoms
14
4.7 Isotopes
Isotopic Symbol

A symbol that not only identifies the element, but
also which isotope it is, and if it is an ion.
A = mass # = (# p+ ) + (# n)
A Q
Z = atomic # = # p+
Z
Q = charge = (# p + ) - (# e -)
X
Indicate the name of the element, and the number of p+ ’s,
n’s and e-’s indicated by the following isotopic symbols:
60
27
Co
238
92
U
37
17
Cl15
4.8 The Periodic Table

Elements are arranged in a pattern in the Periodic Table

An elements position on the table allows us to predict its
properties
Metals
Nonmetals
Metalloids
16
4.8 The Periodic Table

Elements in a column have similar chemical and
physical properties

Columns are called
Groups or Families

Rows are called
Periods

Each period shows
the pattern of
properties repeated
in the next period
17
4.8 The Periodic Table

Main Group

Transition Elements

Inner Transition
Elements

Halogens
part of Period 6 & 7

Noble Gases

Noble Metals


Ag, Au, Pt
18
4.9 Natural States of Elements

Diatomic Molecules: elements that
exist in nature as a pair of atoms
Table 4.5
Element
State at 25 °C
Molecule
Hydrogen
Colorless gas
H2
Nitrogen
Colorless gas
N2
Oxygen
Pale blue gas
O2
Fluorine
Pale yellow gas
F2
Chlorine
Pale green gas
Cl2
Bromine
Reddish liquid
Br2
Iodine
Purple solid
I2
19
4.9 Natural States of Elements
Allotropes

Many solid nonmetallic elements can exist in different forms
with different physical properties, these are called
allotropes

The different physical
properties come from the
different arrangements of
the atoms
Allotropes of carbon:
diamond
graphite
buckminsterfullerene

20
4.10 Ions

Most common pure substances are very poor
conductors of electricity




with the exception of metals and graphite
Water is a very poor electrical conductor
Some substances dissolve in water to form a
solution that conducts well - these are called
electrolytes
When dissolved in water, electrolyte compounds
break up into component ions

ions are atoms or groups of atoms that have an
electrical charge
21
4.10 Ions

Cations: ions that have a positive charge

Anions: ions that have a negative charge

Ions with opposite charges attract

Moving ions conduct electricity
Compound must have no total charge, therefore
we must balance the numbers of cations and
anions in a compound to get 0 total charge




form when an atom loses electrons
form when an atom gains electrons
cations and anions attract each other
22
4.10 Ions

Metals form cations

For each positive charge the ion has 1 less electron
than the neutral atom



Na = 11 e-, Na+ = 10 eCa = 20 e- , Ca+2 = 18 e-
Cations are named the same as the metal


sodium Na →Na+ + 1ecalciumCa →Ca+2 + 2e-
23
4.10 Ions
The most common charge
on a cation can be
determined from the
group numbers for Groups
IA, IIA, IIIA
24
4.10 Ions

Nonmetals form anions

For each negative charge the ion has 1 more
electron than the neutral atom



F = 9 e- , F- = 10 eP = 15 e-, P3- = 18 e-
Anions are named by changing the ending of the
name to -ide


fluorineF + 1e- →Foxygen O + 2e- →O2-
25
4.10 Ions
The charge on an anion
can be determined from
the group number for
Groups 6 & 7
26
4.11 Ionic Compounds

Evidence of Ionic Compounds
27
4.11 Ionic Compounds

Writing Ionic Compound Formulas


There must be cations and anions present
The sum of the charges of the cations & anions must
be zero
Write the formulas for the ionic compounds formed
from the following ions:
K+ and P3Barium ions and oxide ions
Aluminum ions and sulfide ions
28