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Chapter 5
Atoms, Bonding and the Periodic Table
8th Grade Science
Valence Electrons and Bonding
• ____________ - electrons that have the highest energy level and are held most loosely.
• The number of valence electrons that an element has determines the ways in which the atom can _____with other atoms.
• Each element has a specific number of ____________ ranging from 1 to 8.
• ______________ - includes the symbol for the element surrounded by dots that represent the valence electrons.
Valence electrons
Bond
Valence electronsElectron-dot diagram
Elements with more valence electrons are less reactive
Electron Dots and the Periodic Table
Chemical Bonds and Stability
• ____________ - force of attraction that holds two atoms together.
• When atoms bond, ________ may be transferred from one atom to another, or they may be shared between the atoms.
• The result of chemical bonding is a ____________ where a new substance is formed.
Chemical Bond
electrons
Chemical reaction
Relating Periods and Groups
• As the _____________ of an atom increases, the number of electrons increases as you move from the left side of the periodic table to the other.
• Remember: a ________ on the periodic table is a row from left to right.
• A _________ ends when the number of valence electrons equals __.
• The next period will have a higher _________ than the one before.
Atomic Number
period
period8
Energy level
Patterns of Valence Electrons
• Elements within a ______ or a column always have the same number of ____________.
• Group 1 elements have ___ valence electron• Group 2 elements have ___ valence electrons• Each group has one more valence electron than
the one to its ____.• The elements within a group have similar
properties because they all have the same number of ____________ in their atoms.
groupValence electrons
12
left
Valence electrons
Noble Gases
• Group _____• Atoms have ____ valence electrons, except for
Helium• These atoms are ______ - less reactive –
unlikely to transfer or share electrons with other atoms.
18
8
stable
Reactive Metals and Non-metals
• Halogens in Group ___ have ____ valence electrons.
• Halogens are therefore more reactive than the __________.
• Alkali Metals in Group ___ - have ___ valence electron.
• Alkali metals are ___________.How reactive a metal is depends on how easily
its atoms lose valence electrons.
17 7
Noble Gases
1 1
Very reactive
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 _____ to _______.
• Non-metals – most are _____ at room temperature, five are ______, and one is ______
• Non-metals combine with metals by ______ an electron
top bottom
gasessolids
liquid
gaining
Metalloids
• Non-metals combine with other ___________ by ________ electrons
• _________ lie along the zig-zag line between metals and non-metals.
• Metalloids have between ______ valence electrons.
• Metalloids can either _____ or ________ electrons depending on the conditions – behave as both metals and non-metals
Non-metalssharing
metalloids
3 to 6
lose share
Hydrogen
• ____ valence electron• Considered to be a ___________• ___________ but its properties differ greatly
from those of the alkali metals
1
Non-metal
reactive
Ions
• _____ - an atom or a group of atoms with an electric charge.
• When an atom _______ an electron it loses a _______ charge and becomes a ________ ion.
• When an atom _____ an electron, it _____ a negative charge and becomes a _______ ion.
• ____________ - ions that are made of several atoms – have an overall positive or negative charge.
ion
negative positiveloses
gains gainsnegative
Polyatomic ions
Ions and Their Charges
Ionic Bonds
• __________ - the attraction between two 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 bonds
Ionic compound
Sodium Chloride
Chemical Formulas and Names
• _____________ - a combination of symbols that shows the ratio of elements in a compound.
• _____________ - charges of the ions are balanced – the chemical formula represents the balance
• _________ - represents the ratio of elements in the compound. * if there is no subscript – 1 is understood.
Chemical Formula
Ionic compounds
subscript
Naming Ionic Compounds
• The name of the _________ ion comes before the _______ ion.
• Example: magnesium chloride, sodium bicarbonate, sodium oxide
• _______ - negative ion is a single element• ____________ - negative ion is polyatomic –
ammonium nitrate
positivenegative
-ide ending
-ate or ite ending
Chemical formula
-ide ending
Properties of Ionic Compounds
_____________ - hard, brittle crystals with high melting points
When ionic compounds are dissolved in water, they ____________.
_______ - ions form an orderly three dimensional arrangement.
______________ - heat increases energy levels – when ions have enough energy to overcome the attractive forces between them, they break away from each other and melt.
Ionic compounds
Conduct electricity
crystal
High melting points
Electrical Conductivity
• ___________ - flow of charged particles• Ions that are dissolved in water as a result
of___________, are able to move _______ and the solution is able to conduct electricity.
Electric current
Broken bonds freely
Covalent Bonding
• _____________ - chemical bond that is formed when two atoms SHARE electrons.
• Covalent bonds usually form between ___________.
• Ionic Bonds usually form between a _____ and ________
• __________ - neutral group of atoms joined by covalent bonds
Covalent Bond
nonmetals
metal
nonmetal
molecule
Sharing Electrons
Covalent Bonds and Valence Electrons
• The number of _____________that nonmetals can form equals the number of electrons needed to make a total of ____.
• ___________ - is the exception – only needs __.
• Water Molecule – oxygen has __ valence electrons. Hydrogen has __ valence electron. Therefore, oxygen forms two __________ with hydrogen.
eight
Covalent bonds
Hydrogen2
61
Covalent bonds
Double Bonds and Triple Bonds
• A set of eight valence electrons makes the covalent bonded molecule _______
• __________ is the exception – hydrogen only needs ___ electrons to be stable
• ___________ - a chemical bond formed when atoms share two pars of electrons - carbon
• ___________ - a chemical bond formed when atoms share three pairs of electrons - Nitrogen
stable
Hydrogen2
Double bonds
Triple Bonds
Molecular Compounds
• _______________ - a compound that is composed of molecules of atoms that are covalently bonded.
• Molecular compounds have ________________ and ____________ than ionic compounds.
• Molecular compounds DO NOT _____________.
Molecular compound
Lower melting points Boiling points
Conduct electricity
Melting points/ Boiling Points/ Conductivity
• Molecular compounds have ________ attractive forces between molecules.
• Ionic compounds have _____ attractive forces between the molecules
• Therefore, ___energy is needed to melt molecular compounds.
• Molecular compounds do not conduct electricity because there are _____________
weak
strong
less
No charged particles
Polar Bonds / Non-Polar Bonds
• _________ - a covalent bond in which electrons are shared unequally– The atom with the stronger pull will become
slightly ________, the weaker atom will become slightly _______.
_____________ - a covalent bond in which the electrons are shared equally.
Polar Bonds
negativepositive
Non-polar Bonds
Fluorine and Hydrogen
Water = Polar Molecules
Carbon dioxide = non-polar
Alloys
• ____ - 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 ________.
• Alloys are ______ and less likely to react with air or water unlike the pure metals from which they are made.
alloy
metal
stronger
Physical / Chemical Properties
• Physical properties can be different from those of the individual _________ that alloys are made of.
• Depending on how they are mixed, alloys retain many of the __________ properties of metals.
• Elements like iron are often mixed with other elements such as carbon, nickel, and chromium to prevent _____ - a chemical reaction that occurs when iron is exposed to air or water – examples = steel used in forks.
elements
physical
rusting
Metallic Bonding
• Metals _______ electrons easily because their __________ electrons are not strongly held.
• Metal atoms are held very closely and in a specific arrangement – metals exist as _______
• Each metal ion is held in the ______ by a ___________.
• ___________ - an attraction between a positive metal ion and the valence electrons surrounding it.
lose
valence
crystals
crystal
Metallic bond
Metallic bond
Metallic Bonds Continued
• Solid metals consist of positively charged ions surrounded by loose _______________.
• The _____ valence electrons an atom can add the _______ the metallic bond.
• Question: Which are stronger metallic bonds or ionic bonds?
Valence electrons
metal
stronger
Metallic Properties
• _____________ explains many of the common physical properties of metals and their alloys.
• _____________ - metals can be stretched, compressed, or pushed into different shapes because the __________ 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.
Metallic Bonding
Changes in shape
Positive ions
Other Metallic Properties
• _________________ - metals conduct electricity easily because their electrons can move freely among the atoms.– When connected to a battery, the _________ will
run into the metal at a certain point and out of the metal at another point.
________ - polished metals are shiny and reflective. When light hits a metal’s _____________ they absorb the light and give it off again.
Electrical conductivity
current
lusterValence electrons
Heat Conductivity
• Heat causes particles of matter to move ______
• If these particles collide with cooler particles of matter, thermal ______ is transferred to the cooler particles.
• _____________ valence electrons transfer energy from nearby atoms and other electrons – heat travels easily through a metal or a metal alloy.
faster
energy
Freely moving
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