8th Grade – Chapter 5

Report
Chapter 5
Atoms, Bonding and the Periodic
Table
8th Grade Science
Valence Electrons and Bonding
electrons - electrons that have the highest
• Valence
____________
energy level and are held most loosely.
• The number of valence electrons that an element
has determines the ways in which the atom can
Bond
_____with
other atoms.
• Each element has a specific number of
Valence electrons ranging from 1 to 8.
____________
Electron-dot diagram - includes the symbol for the
• ______________
element surrounded by dots that represent the
valence electrons.
Elements with more valence electrons
are less reactive
Electron Dots and the Periodic Table
Chemical Bonds and Stability
• ____________
- force of attraction that holds
Chemical Bond
two atoms together.
electrons may be
• When atoms bond, ________
transferred from one atom to another, or they
may be shared between the atoms.
• The result of chemical bonding is a
Chemical reaction where a new substance is
____________
formed.
Relating Periods and Groups
• As the _____________
of an atom increases, the
Atomic Number
number of electrons increases as you move from
the left side of the periodic table to the other.
period
• Remember: a ________
on the periodic table is a
row from left to right.
period
• A _________
ends when the number of valence
8
electrons equals __.
Energy level
• The next period will have a higher _________
than the one before.
Patterns of Valence Electrons
• Elements within a ______
or a column always
group
electrons
have the same number of Valence
____________.
• Group 1 elements have ___
valence electron
1
• Group 2 elements have 2___ valence electrons
• Each group has one more valence electron
than the one to its ____.
left
• The elements within a group have similar
properties because they all have the same
number of ____________
Valence electrons in their atoms.
Noble Gases
18
• Group _____
• Atoms have ____
valence electrons, except for
8
Helium
stable
• These atoms are ______
- less reactive –
unlikely to transfer or share electrons with
other atoms.
Reactive Metals and Non-metals
• Halogens in Group ___
valence
17 have ____
7
electrons.
• Halogens are therefore more reactive than the
Noble Gases
__________.
1
• Alkali Metals in Group ___
- have ___
valence
1
electron.
Very reactive
• Alkali metals are ___________.
How reactive a metal is depends on how easily
its atoms lose valence electrons.
Other Metals and Non-Metals
• The reactivity of metals decreases from left
to right across the periodic table.
• In Groups one and 2, reactivity increases from
top
bottom
_____
to _______.
gases at room
• Non-metals – most are _____
temperature, five are ______,
and one is
solids
______
liquid
• Non-metals combine with metals by ______
gaining
an electron
Metalloids
• Non-metals combine with other ___________
Non-metals
sharing
by ________
electrons
• _________
lie along the zig-zag line between
metalloids
metals and non-metals.
3 to 6
• Metalloids have between ______
valence
electrons.
lose
share
• Metalloids can either _____
or ________
electrons depending on the conditions –
behave as both metals and non-metals
Hydrogen
1
• ____
valence electron
• Considered to be a ___________
Non-metal
• ___________
but its properties differ greatly
reactive
from those of the alkali metals
Ions
• _____
- an atom or a group of atoms with an
ion
electric charge.
• When an atom _______
an electron it loses a
loses
negative charge and becomes a ________
positive
_______
ion.
gains
• When an atom gains
_____ an electron, it _____
a
negative charge and becomes a _______
negative ion.
Polyatomic ions - ions that are made of several
• ____________
atoms – have an overall positive or negative
charge.
Ions and Their Charges
Ionic Bonds
• __________
- the attraction between two
Ionic bonds
oppositely charged ions.
• Ionic bonds form as the result of the
attraction between positive and negative
ions
• A compound that consists of both positive and
negative ions (sodium chloride) is an
______________.
Ionic compound
Sodium Chloride
Chemical Formulas and Names
• _____________
Chemical Formula - a combination of symbols
that shows the ratio of elements in a
compound.
• _____________
- charges of the ions are
Ionic compounds
balanced – the chemical formula represents
the balance
• _________
- represents the ratio of elements
subscript
in the compound. * if there is no subscript – 1
is understood.
Naming Ionic Compounds
positive
• The name of the _________
ion comes before
negative
the _______
ion.
• Example: magnesium chloride, sodium
bicarbonate, sodium oxide
• _______
-ide ending - negative ion is a single element
-ate or ite ending - negative ion is polyatomic –
• ____________
ammonium nitrate
Chemical formula
-ide ending
Properties of Ionic Compounds
_____________
Ionic compounds - hard, brittle crystals with high
melting points
When ionic compounds are dissolved in water, they
____________.
Conduct electricity
_______
- ions form an orderly three dimensional
crystal
arrangement.
High melting points - heat increases energy levels –
______________
when ions have enough energy to overcome the
attractive forces between them, they break away
from each other and melt.
Electrical Conductivity
• ___________
Electric current - flow of charged particles
• Ions that are dissolved in water as a result
of___________,
are able to move _______
Broken bonds
freely
and the solution is able to conduct electricity.
Covalent Bonding
Covalent Bond
• _____________
- chemical bond that is
formed when two atoms SHARE electrons.
• Covalent bonds usually form between
___________.
nonmetals
metal
• Ionic Bonds usually form between a _____
and ________
nonmetal
• __________
- neutral group of atoms joined
molecule
by covalent bonds
Sharing Electrons
Covalent Bonds and Valence Electrons
• The number of _____________that
nonmetals
Covalent bonds
can form equals the number of electrons
eight
needed to make a total of ____.
• ___________
- is the exception – only needs
Hydrogen
__.
2
• Water Molecule – oxygen has __
6 valence
electrons. Hydrogen has __
1 valence electron.
Therefore, oxygen forms two __________
Covalent bonds
with hydrogen.
Double Bonds and Triple Bonds
• A set of eight valence electrons makes the
covalent bonded molecule _______
stable
• __________
is the exception – hydrogen only
Hydrogen
needs ___
2 electrons to be stable
Double bonds
• ___________
- a chemical bond formed when
atoms share two pars of electrons - carbon
• ___________
- a chemical bond formed when
Triple Bonds
atoms share three pairs of electrons - Nitrogen
Molecular Compounds
Molecular compound - a compound that is
• _______________
composed of molecules of atoms that are
covalently bonded.
• Molecular compounds have
Lower melting points
Boiling points
________________
and ____________
than
ionic compounds.
• Molecular compounds DO NOT
Conduct electricity
_____________.
Melting points/ Boiling Points/
Conductivity
weak
• Molecular compounds have ________
attractive forces between molecules.
strong attractive forces
• Ionic compounds have _____
between the molecules
• Therefore, less
___energy is needed to melt
molecular compounds.
• Molecular compounds do not conduct
electricity because there are _____________
No charged particles
Polar Bonds / Non-Polar Bonds
Polar Bonds - a covalent bond in which
• _________
electrons are shared unequally
– The atom with the stronger pull will become
negative
slightly ________,
the weaker atom will become
slightly _______.
positive
Non-polar Bonds - a covalent bond in which the
_____________
electrons are shared equally.
Fluorine and Hydrogen
Water = Polar Molecules
Carbon dioxide = non-polar
Alloys
alloy - a mixture made of two or more
• ____
elements that has the properties of metal
• In every alloy at least one of the elements is a
________.
metal
• Alloys are ______
stronger and less likely to react with
air or water unlike the pure metals from which
they are made.
Physical / Chemical Properties
• Physical properties can be different from those of
the individual _________
that alloys are made of.
elements
• Depending on how they are mixed, alloys retain
physical
many of the __________
properties of metals.
• Elements like iron are often mixed with other
elements such as carbon, nickel, and chromium
to prevent _____
rusting - a chemical reaction that
occurs when iron is exposed to air or water –
examples = steel used in forks.
Metallic Bonding
• Metals _______
electrons easily because their
lose
__________
electrons are not strongly held.
valence
• Metal atoms are held very closely and in a
crystal
specific arrangement – metals exist as _______
crystals by a
• Each metal ion is held in the ______
Metallic bond
___________.
• ___________
Metallic bond - an attraction between a positive
metal ion and the valence electrons surrounding
it.
Metallic Bonds Continued
• Solid metals consist of positively charged ions
surrounded by loose _______________.
Valence electrons
metal valence electrons an atom can add
• The _____
the _______
stronger the metallic bond.
• Question: Which are stronger metallic bonds
or ionic bonds?
Metallic Properties
• _____________
Metallic Bonding explains many of the common
physical properties of metals and their alloys.
Changes in shape - metals can be stretched,
• _____________
compressed, or pushed into different shapes
because the __________
Positive ions are attracted to the
loose electrons all around them rather than to
other metal ions.
– Metallic bonds between the ion and the surrounding
electrons keep the metal from breaking.
Other Metallic Properties
Electrical conductivity
• _________________
- metals conduct
electricity easily because their electrons can
move freely among the atoms.
– When connected to a battery, the _________
will
current
run into the metal at a certain point and out of the
metal at another point.
________
- polished metals are shiny and reflective.
luster
When light hits a metal’s _____________
Valence electrons they
absorb the light and give it off again.
Heat Conductivity
• Heat causes particles of matter to move
faster
______
• If these particles collide with cooler particles
of matter, thermal ______
energy is transferred to the
cooler particles.
• _____________
valence electrons transfer
Freely moving
energy from nearby atoms and other
electrons – heat travels easily through a metal
or a metal alloy.
Growing Copper Sulfate Crystals
• Materials: One egg, plastic container, measuring apparatus, spoon for
stirring, and copper sulfate
• Procedures:
• 1 Crack an egg carefully to get two fairly even halves. Discard the inside of
the egg and gently wash the shell in warm water.
• 2 Place the eggshells in a plastic container on a paper towel. LABEL
• 3 Pour 0.25 cups of hot water into a clean glass jar. Add 1 to 1.5 tsp. of
copper sulfate to the water and stir with a spoon.
• 4 Carefully pour the copper sulfate solution into the halves of the
eggshells. Place the container with the eggshells in the chemical hood.
• 5 Let the solution sit in the eggshells for several days until the desired
amount of crystals have formed.
• 6 Look at crystals under the microscope

similar documents