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Chemical Foundations and Elements, Atoms, and
Ions
4.1 Elements
 All chemical matters contain elements
 Presently 115 different known elements
 88 are occurred naturally
 9 elements account for the most of the compounds
found in earth’s crust
 Elements can not broken down further
 Distinguish by atomic number
Elements and the Earth’s Crust
Symbols of Elements
 Derived from Greek, Latin and German
 Describe the properties of element
 E.g Gold – Au (Aurum –shining dawn)

Sodium – Na (Natrium)
 Use abbreviation to simplify the written word
 1st letter must be capitalized
 E.g
Fluorine
Carbon
Zinc
Iron
Phosphorous
F
C
Zn
Fe
P
Natural of Matter
 Most natural materials are mixtures of pure substances
 Pure substances are either elements or combination of
elements called compounds
 Law of constant composition: a given compound always
has the same composition, regardless of where it comes
from
 E.g
Water always contains 8 g of Oxygen for every 1 g
of hydrogen
4.3 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 are different from those of any other
elements
4.3 Dalton’s Atomic Theory
 Atoms of one element can be 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 process. Atoms can not
be created or destroyed in a chemical reactions. A Chemical
reaction simply changes the way atoms are grouped
together.
4.4 Formulas of Compounds
 Compound: a substance that is composed of the atoms of
two or more elements
 Contains exactly the same relative mass
 Chemical Formula: expresses the type of atoms and the
number of each type of unit
 Short, convenient and easier to recognize
Rules for Writing Formulas
 Each atom present is represented by its element symbol
 The number of each type of atom is indicated by a
subscript written to the right of the element symbol
 When only on atom of a given is present, the subscript 1 is
not written
Writing Formulas of Compounds
 Write the formula for each of the following
compounds, listing the elements in the order given
 Each molecule of a compound that has been implicated in the
formation of acid rain contains one atom of sulfur and three
atoms of oxygen
 A molecule containing six carbon atoms and six hydrogen
atoms
 A molecule contains one aluminum atom and three chlorine
atoms
 A compound containing equal numbers of sodium and
nitrogen atoms, but three times as many oxygen atoms as
nitrogen atoms
4.5 – 4.6 Structure of the Atom
Structure of the Atom
 Atoms are the tiny particles that made up an element
 Building block of matter
 Contains nucleus with neutrons and protons
 Protected by an electron cloud
Electrons
 Thomson- Found that cathode ray consists of tiny,
negatively charged particles called electrons.



Electrons are emitted from electrodes made of two thin pieces of
metal
Many different metals may be used to make electrodes
 Different metals contain different electrons
Cathode rays can be deflected by bringing either a magnet or an
electrically charged plate near tube. This deflection depends on
 the strength of deflecting magnetic or electric field
 the size of the negative charge on the electron
 the mass of electron
Electron
Nucleus of the Atom
 Nucleus – any tiny
central core in an atom
where the mass of the
atom is concentrated.
 contains the atoms positive
charges

Electrons move in space
relatively large distance away
from the nucleus.
Nucleus of the Atom
 Nucleus is composed of
two kinds of particles.
 Protons have a mass of
1.672623 x 10-24 g and are
positive charge

numbers of protons equal to
number of electrons in a
neutral atom.
 Neutrons – almost
identical in mass to proton
but carry no charge
Structure of the Atom
Particle
Symbol
Charge
Mass
electron
e-
-1
0.0005486
amu
proton
p+
+1
1.007276 amu
neutron
no
0
1.008665 amu
4.7 Isotopes
 All atoms of the same element have the same number of
protons and the same number of electrons
 In a free atom or neutral atom, the positive charges and
negative charges always yield a net zero charge
 Atoms with the same number of proton but differ number
of neutrons is called Isotope
Atomic Numbers
Elements differ from one another according to the
number of protons in their atoms


Atomic number (Z) = the number of protons in an atom
= the number of electrons in an atoms
Mass Number

Mass number (A) = number of proton (Z) + number
of neutrons (N)
Isotopes
Atoms with identical atomic numbers but different
mass number





Mass number is written as a superscript on the top left
Atomic number is written as a subscript on the bottom
left. (The atomic number is sometimes left off since all
atoms of an element always contain the same number of
protons)
The number of neutrons in an isotope can be calculated
from A-Z
Number of neutrons in an atom has little effect on the
chemical properties of the atom
Isotope
A X
Z
Or
X-A
Examples
 Write the symbol for the magnesium atom (atomic number
12) with a mass number of 24. How many electrons and
how many neutrons does this atom have?
 Write the symbol for the silver atom (Z = 47) that has 61
neutrons
 The krypton atom has 48 neutron
Example
 Given the number of protons, neutrons and electrons in the
following atom

60

37 Cl
17
201 Hg
80

27Co
4.8 Development of the Periodic Table
 A.
Creation of the Periodic table






1.
2.
3.
4.
5.
6.
Ideal example of how scientific theory comes into being
Random observation
Organization of data in ways that make sense
Consistent hypothesis emerges
Explains known facts
Makes predictions about unknown phenomena
Development of the Periodic Table
 Mendelee's hypothesis about organizing known chemical
information
1. Met criteria for a good hypothesis
2. Listed the known elements by atomic weight
3. Grouped them together according to their chemical reactivity
Periodic Table
 Periods:







the horizontal
row (7)
Groups:
the vertical
column (18)
*elements in the same group
have similar chemical
properties.
The Periodic table
Group 1A – Alkali Metals
Group 2A – Alkaline Metals
Group 7A – Halogens
Group 8A - Noble Gases
Physical Properties
 Metals:
 Largest category of
elements; found on the left
side of the periodic table
(left of the heavy zigzag
line)
 Solids (except mercury)
 Malleable
 Ductile – can be drawn
into thin wires without
breaking
 Conduct heat and
electricity
 Nonmetals
 Found on the right side of the




periodic table (right of the
heavy zigzag line).
Gases, liquids, or solids -11 of
17 nonmetals are gases, one is
liquid (Br) and only five are
solid at room temperature (C, P,
S, Se and I)
Brightly colored
Brittle solids
Poor conductors of heat and
electricity
4.8 Introduction to the Periodic Table
Example
 For each of the following elements, use the periodic
table in the next slide to give the symbol and atomic
number and to specify whether the element is a metal or
nonmetal. Also give the named family to which the
element belongs (if any)
 Iodine
 Strontium
 Lithium
 Xeon
4.9 Natural States of the Elements
 Diatomic molecules
 Molecules made up to two
atoms of either the same
of different elements
 E.g O2, N2, H2 , CO etc…
 few diatomics are found to
occur naturally on Earth
outside of laboratories
4.10
Ions
 Ions – charged particles resulting from the loss or
gain of electron
Cation – positively particles resulting from the loss of

electrons

Na(s)  Na+ + e-(aq)
Anion – negatively charge particle resulting from the gain

of one or more electrons

Cl(s) + e-  Cl-(aq)
Polyatomic ions – charged, covalently bonded groups of

atoms

Charged molecules – consist of specific numbers and kinds of
atoms joined together by covalent bonds in a definite way

NO3-(aq), -OH(aq)
Ion Charges and the Periodic Table
The charge on the ion depends on the group number

Main-group metal cations: charge = group number
Group IA = +1 (M 1+ )



Group IIA = +2 (M 2+ )
Group IIIA = +3 (M3+)
Main group nonmetal anions: charge = group number 8




Group VA = 5 -8 = -3
Group VIA = 6 -8 = -2
Group VIIA = 7 – 8 = -1
Example
 Determine the charge of each of the following ions and
write out its symbol
 Magnesium
 Oxygen
 Cesium
 Nitrogen
 Bromide
Examples
 How many electrons are contained in each of the following
ions?
a. Fe2+
c. S2-
b.
d.
Co3+
N 3-
4.11 Ionic Solid
 Ionic solids – cations and anions are packed together in a
regular manner so that the charges cancel.
 Na+(aq) + Cl-(aq)  NaCl(s)
 Mg2+ (aq) + 2Cl-(aq)  MgCl2(s)
Ionic Compounds
Example
 Use the pairs of ions below to give the formula for the
compound containing these ions
 Ca2+
 Al 3+
 Mg2+
 K+
and Cland S2and N3and
O2-