Download c. Section 3.3 Elements and the Periodic Table

Chapter 9: Elements are the Building
blocks of Life
Section 9.1- Elements and the
Periodic Table
Keep Scale in mind…
Animation:
http://htwins.net/scale2/
I. ELEMENTS
• All matter is made up of one or more
elements or a mixture of elements
• An element is a pure substance made
out of any one kind of atom.
ex. gold is made up of gold atoms only
ex. carbon monoxide is made up of
carbon atoms and oxygen atoms and
so is NOT an element
• At room temperature (250C), elements may be in
solid, liquid, or gas state
Only 92 occur naturally!
• There are over 115 types of elements. Each
element has a specific number of electrons and
protons.
ex. carbon has 6 electrons/protons
ex. oxygen has 8 electrons/protons
ex. hydrogen has 1 electron/proton
II. CHEMICAL SYMBOLS
• Each element is represented by one or two letters taken from its
Latin name or Greek name.
• The first letter is always capitalized. The second letter (if there is
one), is always lower case. This is called the chemical symbol and it
is used by scientists in all languages.
ex. H stands for hydrogen
ex. Hg stands for mercury
(from latin word hydrargyrum,
meaning liquid silver)
• Symbols can also be used to show the
proportion of each element in a compound
ex. H2O = two parts hydrogen and one part
oxygen
9.2- The PT and Chemical Properties
I. PERIODIC TABLE
• All known elements are listed in a giant table
called the periodic table.
• The periodic table lists each element name,
symbol, atomic number, atomic mass, and ion
charge(s)
• Did You Know?
• Most of your body’s mass is
made up of:
65% oxygen
18% carbon
10% hydrogen
3% nitrogen
2 % calcium
trace other elements
ATOMIC NUMBER: the number of protons in the
nucleus of an element.
• always a whole number.
• the number of protons equals the number of
electrons, unless the atom is an ion, or charged.
• there are no ions in the periodic table- everything is
shown in its neutral state.
ATOMIC MASS/MASS NUMBER: the mass of an
average atom of an element.
• measures the number of protons and
neutrons.
• is written in a decimal form and uses the
atomic mass unit (amu).
• the number of neutrons can vary from atom
to atom, so atomic mass may not be a whole
number as it represents the average.
You Try….
Write the chemical symbol
for Madeitupium:
7 protons
8 neutrons
7 electrons
A=
B=
C=
D=
Chemical Symbol:
Atomic number:
Atomic weight/mass:
• Here is an example of hydrogen and three
possible scenarios.
• Hydrogen can have no
neutrons, one neutron,
or two neutrons.
• An isotope is an atom
that has the same
number of electrons
and protons but a
different number of
neutrons.
How many neutrons in Carbon?
Atomic weight (mass)= 12.01 (= p + n)
Atomic number = 6 (=p only)
# of neutrons = 12 - 6 = 6 neutrons
• Ion Charge: this is an electric charge that forms
on an atom when it gains or loses electrons. A
charged atom is called an ion.
• If an atom…
….gains electrons, it becomes negatively charged
has more electrons than protons
….loses electrons, it becomes positively charged
has more protons than electrons
• An ion is designated with a charge in the top right
region of the symbol. Ex. O2-
IV. CLASSIFICATION of ELEMENTS
• Properties of any element are specific to that
element
• Properties are used to group similar elements
together
• Three major classification groups are:
1. METALS
2. NON-METALS
3. METALLOIDS (semi-metals)
Metalloids are elements that share some
properties of metals and some of non-metals.
Malleability: ability to
beat into sheets
Ductility: ability to be drawn
into wires
• All metals appear on the left side of the
periodic table
• All non-metals appear on the right side of the
periodic table
• The metalloids form a diagonal line between
metals and non-metals, often called the
staircase
What about
hydrogen????
• Note that in chemical reactions, metals tend to
form positive ions, or cations, while non-metals
tend to form negative ions, or anions.
III. PERIODS AND FAMILIES
• Period = horizontal row, numbered 1-7
• Family or Group = vertical columns, #1-18
• The period tells you how many shells (rings)
there are in the Bohr model
Ex. Lithium (Li) is in the 2nd period and so has 2 rings
Ex. Magnesium (Mg) is in the 3rd period and so has 3 rings
• The chemical family indicates the number of
electrons in the outer shell
Ex. Lithium (Li) is in the 1st family, so it has 1 electron
in the outer shell
Ex. Magnesium (Mg) is in the 2nd family, so it has
2 electrons in the outer shell
Some families you should know…
1. ALKALI METALS- family #1- HIGHLY reactive, soft,
react with oxygen and water, low melting points.
• Members include: Li, Na, K, Rb, Ca, Fr
2. ALKALINE EARTH METALS- family #2- less reactive
than alkali metals, burn if heated and used in
fireworks
• Members include: Be, Mg, Ca, Sr, Ba, Ra
3. HALOGENS- family #17- highly reactive nonmetals
• Members include: F, Cl, Br, I, At
4. NOBLE GASES- family #18- VERY, VERY STABLE
• Members include: He, Ne, Ar, Kr, Xe, Rn
General trends…
1. The atomic number increases
one by one through the period
table, left from right, top to
bottom.
2. The atomic mass tends to
increase along with the atomic
number but there are some
exceptions (e.g. cobalt and
nickel)
3. Elements on the left side of the table
generally form positive ions.
• Elements on the right side, except for the last
column, tend to form negative ions.
• Elements in the same column often form ions
with the same charge as other elements in
that column.
9.3 The PT and Atomic Theory
I. Patterns in the Periodic Table
• The patterns we have seen in the periodic
table are not a just coincidence!
• The properties of elements are determined by
the electrons in the outer shells.
• Elements with similar properties line up in
columns because all those elements have the
same number of electrons in the outer shell
II. Drawing Bohr Models
• The BOHR MODEL is a diagram that we use to show the
electrons in each shell
• Each electron shell (layer) has a maximum number of
electrons it can hold
1st shell  up to 2 electrons
2nd shell  up to 8 electrons
3rd shell  up to 8 electrons
4th shell  up to 18 electrons
• This pattern of electrons is followed by all atoms, although
not all atoms have that many electrons.
• Electrons are usually drawn in pairs, if
possible. Also, electrons must fill up the entire
inner shell before moving to the outer shell.
• There are various ways to write a Bohr
diagram, but for science 8 you should include:
– chemical symbol
– Number of protons
– Show where the electrons are in the shells
You are expected to be able to draw
Bohr Models….
III. Valence Shells
• the electrons in the outermost shell are called
valence electrons. These electrons have the
greatest influence on the properties of an atom.
• -the shell that contains valence electrons is called
the valence shell.
• same family  same # of valence electrons
• same period  SAME # of shells that have
electrons
Try This:
Sketch a Bohr Model for….
a) Helium
b) oxygen
c) Boron
• Why are the noble gases so stable?
– Their outer shell is full of electrons!
– In order for atoms to react with other atoms, they
must give/take/share electrons. Noble gases DO
NOT do this.
• Atoms always want to be stable. They will
take/give electrons from other atoms to fill up
their outer shell.
• Recall…
Metals tend to lose electrons
( + ion)
Did you know? Metal Ions burn different colours…
Non-metals tend to gain electrons ( - ion)
Once an atom has gained/lost electrons, it
becomes charged (= ion)
• Ions are written by giving the symbol of the
element followed by a superscript showing
the charge
Ex.
Li loses an electron to become positive Li+
(3 protons, 2 electrons)
Mg loses two electrons to become positive Mg2(12 protons, 10 electrons)
Cl gains one electron to become negative
(17 protons, 18 electrons)
Cl-
Section 9.4 Elements Combine to
Form Compounds
Section 9.4 Compounds
• COMPOUND: a pure substance made up of more
than one kind of element in which the elements
are joined together (= chemical bonds)
• CHEMICAL BONDS: link between two or more atoms that hold the atoms together
• There are two types of compounds:
– covalent compounds
– ionic compounds
I. Covalent Compounds
• Always between two non-metals
• Atoms combine by sharing electrons and
make molecules
Examples: H20
Covalent Compounds Share!
You will not need to know anything beyond this for Science 8!
II. Ionic Compounds
• Between metal and non-metal
• Atoms give or take electrons and make ions
Example: table salt (NaCl)
Na + Cl  NaCl
• Ionic compounds exist as a solid in the
form of an ionic lattice (a repeating
pattern of positive and negative ions).
• This is because all the positive ions attract
all the negative ions and repel other
positive ions.
Ionic Compounds Give and Take!
In summary: