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