4.1 Atomic Theory and Bonding Atomic Theory - askmryuenaskmryuen.com/askmryuen2007/science10new/BC10_Chapter_4.pdf · 4.1 Atomic Theory and Bonding ... Atomic Theory • Atoms are

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(c) McGraw Hill Ryerson 2007

4.1 Atomic Theory and Bonding

• An atom is the smallest particle of an element that still has the properties of that element

50 million atoms, lined up end to end = 1 cmAn atom = proton(s) + neutron(s) + electron(s)

• Atoms join together to form compounds.A compound is a pure substance that is composed of two or more atoms combined in a specific way.Oxygen and hydrogen are atoms/elements; H2O is a compound.

• A chemical change occurs when the arrangement of atoms in compounds changes to form new compounds.

See pages 168 - 169


Atomic Theory

• Atoms are made up of smaller particles called subatomic particles.

• The nucleus is at the centre of an atom.The nucleus is composed of protons and neutrons.Electrons exist in the space surrounding the nucleus.# of protons = # of electrons in every atomNuclear charge = charge on the nucleus = # of protonsAtomic number = # of protons = # of electrons See page 170


Organization of the Periodic Table

• In the periodic table elements are listed in order by their atomic number.

Metals are on the left (the transition metals range from group 3 to group 12), non-metals are on the right, and the metalloids form a “staircase” toward the right side.Rows of elements (across) are called periods.

All elements in a period have their electrons in the same general area around their nucleus.

Columns of elements are called groups, or families.All elements in a family have similar properties and bond with other elements in similar ways.Group 1 = alkali metalsGroup 2 = alkaline earth metalsGroup 17 = the halogensGroup 18 = noble gases

See page 171


The Periodic Table

Where are the following?• Atomic

number

• Period

• Group/Family

• Metals

• Non-metals

• Transition metals

• Metalloids

• Alkali metals

• Alkaline earth metals

• Halogens

• Noble gases

See page 172

INC

REA

SIN

G R

EAC

TIVI

TY


Periodic Table and Ion Formation

• Atoms gain and lose electrons to form bonds.The atoms become electrically charged particles called ions.Metals lose electrons and become positive ions (cations).

Some metals (multivalent) lose electrons in different ways.For example, iron, Fe, loses either two (Fe2+) or three (Fe3+) electrons

Non-metals gain electrons and become negative ions (anions).Atoms gain and lose electrons in an attempt to have the same number of valence electrons (electrons farthest from the nucleus) as the nearest noble gas in the periodic table.

See page 173

~ ~


Bohr Diagrams

• Bohr diagrams show how many electrons appear in each electron shell around an atom.

Electrons in the outermost shell are called valence electrons.Think of the shells as being 3-D like spheres, not 2-D like circles.

See page 174

What element is this?

• It has 2 + 8 + 8 = 18 electrons, and therefore, 18 protons.

• It has three electron shells, so it is in period 3.

• It has eight electrons in the outer (valence) shell.

18 p

22 n

argon

2


Patterns of Electron Arrangement in Periods and Groups

• Electrons appear in shells in a very predictable manner.• There is a maximum of two electrons in the first shell, eight in the

2nd shell, and eight in the 3rd shell.The period number = the number of shells in the atom.Except for the transition elements, the last digit of the group number = the number of electrons in the valence shell.

See page 175

The noble gas elements have full electron shells and are very stable.


Forming Compounds

• When two atoms get close together, their valence electrons interact.If the valence electrons can combine to form a low-energy bond, a compound is formed.Each atom in the compound attempts to have the stable number of valence electrons as the nearest noble gas.Metals may lose electrons and non-metals may gain electrons (ionic bond), or atoms may share electrons (covalent bond).

• Ionic bonds form when electrons are transferred from positive ions to negative ions.

• Covalent bonds form when electrons are shared between two non-metals.

Electrons stay with their atom but overlap with other shells.

See pages 176 - 177


Forming Compounds (continued)

• Ionic bonds are formed between positive ions and negative ions.Generally, this is a metal (+) and a non-metal (-) ion.For example, lithium and oxygen form an ionic bond in the compound Li2O.

• Covalent bonds are formed between two or more non-metals.Electrons are shared between atoms.

See pages 176 - 177

lithium oxygen

+

Electrons are transferred from the positive ions to negative ions

Li+ O2- Li+lithium oxide, Li2O

hydrogen fluorine

+

electrons are shared

Hydrogen fluoride


Lewis Diagrams

• Lewis diagrams illustrate chemical bonding by showing only an atom’s valence electrons and the chemical symbol.

Dots representing electrons are placed around the element symbols at the points of the compass (north, east, south, and west).Electron dots are placed singly until the fifth electron is reached then they are paired.

See page 178


Lewis Diagrams of Ions

• Lewis diagrams can be used to represent ions and ionic bonds.For positive ions, one electron dot is removed from the valence shell for each positive charge.For negative ions, one electron dot is added to each valence shell for each negative charge. Square brackets are placed around each ion to indicate transfer of electrons.

See page 179

Be Cl• •

• •• •

• •

• •• •• •

• •

Each beryllium has two electrons to transfer away,

and each chlorine can receive one more electron.

BeCl Cl• •

• •• •

• •

• •• •• •

• •

• •• •• •

• •

BeCl Cl• •

• •• •

• •

• •• •• •

• •

• •• •• •

• •

Since Be2+ can donate two electrons and each Cl– can

accept only one, two Cl– ions are necessary.

beryllium chloride

2+ ––


Lewis Diagrams of Covalent Bonds

• Lewis diagrams can also represent covalent bonds.Like Bohr diagrams, valence electrons are drawn to show sharing of electrons.The shared pairs of electrons are usually drawn as a straight line.

See page 179

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Lewis Diagrams of Diatomic Molecules

See page 180

• •• •• •

• •

O• •

• •• •

• •

O• •

• •• •

• •

O• •

• •• •

• •

O• •

• •• •

• •

O• •

• •• •

• •

O

Several non-metals join to form diatomic molecules.

Valence electrons are shared, here in two

pairs.

This is drawn as a double bond.

• Diatomic molecules, like O2, are also easy to draw as Lewis diagrams.

Take the Section 4.1 Quiz (c) McGraw Hill Ryerson 2007

• Covalent molecules share electrons.There is generally no order to the formation of covalent molecules.These molecules clump together as solids, liquids or gases.Covalent molecules are like a play-pit full of plastic balls.

Each plastic ball = 1 covalent molecule of H2O

4.2 Names and Formulas of Compounds

• Ionic compounds are made up of positive and negative ions.All of the positive and negative ions organize in a pattern.

Negative-positive attract.Negative-negative and positive-positive repel.

Ionic compounds form from the inside out as solid crystals.Ionic compounds are like a solid stack of bricks.

A salt shaker contains thousands of small pieces of NaCl.

See pages 184 - 185

Salt, NaCl

Water, H2O


The Chemical Name and Formula of an Ionic Compound

• Ionic compounds are composed of positive ions and negative ions.The name of an ionic compound = positive ion + negative ion-ide.For example, an ionic compound forms between magnesium and oxygen.

The positive ion is the first part of the name, magnesium.The negative ion forms part of the ending of the name, oxygen.Add -ide to the end of the name to form magnesium oxide.

• Ionic formulas are based on the ions of the atoms involved.Remember the naming principles above.For example, what is the name of Ca3N2?

Ca, the positive ion, is calcium.N, the negative ion, is nitrogen.Drop the end of the anion and add -ide.Calcium nitride

See pages 186 - 187

Magnesium oxide is used

as a drying agent.


The Chemical Name and Formula of an Ionic Compound (continued)

• Writing formulas for ionic compounds:In an ionic compound, the positive charges balance out the negative charges.The ratio of positive:negative charges gives the proper formula.

The ratio is always written in reduced form.For example, what is the formula for magnesium phosphide?

See page 188

magnesium is Mg2+ phosphorous is P3–

Lowest common multiple of 2 and 3 is 63 Mg2+ ions and 2 P3– ionsMg3P2

Try the formula for calcium oxide.calcium is Ca2+ oxygen is O2–

1 Ca2+ ion and 1 O2– ionsCa2O2, which is simplified and written as CaO

Calcium oxide, also known as

“quicklime” was once produced by cooking limestone

in ancient kilns.


Formula of an Ionic Compound with a Multivalent Metal

• Some transitional metals are multivalent, meaning they have more than one ion form.

On the periodic table, the most common form of the ion is listed on top.In the name of the compound, Roman numerals are used following the positive ion to indicate which ion was used.For example, what is the formula manganese (III) sulphide?

See pages 189 - 191

This manganese is Mn3+. sulfur is S2–

Lowest common multiple of 3 and 2 is 62 Mn3+ ions and 3 S2– ionsMn2S3

titanium is Ti4+ or Ti3+ fluorine is F–

1 Ti4+ ion and 4 F– ionstitanium (IV) fluoride

Try the name for TiF4


Polyatomic Ions

• Some ions, called polyatomic ions, are made up of several atoms joined together with covalent bonds.

The whole group has a + or – charge, not the individual atoms.

See pages 192 - 193

What is the formula of sodium sulphate?

What is the name of the compound KClO?

Na+ and SO42– Na2SO4

K+ = potassium ClO– = hypochlorite

potassium hypochlorite

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Names and Formulas of Covalent Compounds

• Covalent compounds, also called molecules, rely on the chemical formula to reveal the components of the molecule.

Covalent compounds are made up of two or more non-metals.Names may reveal the components, but often they do not.Subscripts mean something different in covalent compounds

Ionic compounds subscripts show the smallest whole-number ratio between the ions in the compound.Covalent molecules have subscripts that show the actual number of atoms in the molecule.

See page 193

What is the chemical formula for the molecule ethanol?

What is the name of the molecule C12O22H11?

C2H6O, a name that must be memorized or looked up when needed.

Sucrose, also called table sugar.(c) McGraw Hill Ryerson 2007

Naming Binary Covalent Compounds

• Binary covalent compounds (two non-metal atoms) use a system of prefixes.

See pages 194 - 195

What is the chemical formula for the molecule trinitrogen tetrachloride?

What is the name of the molecule Si3P6?

N3Cl4

Trisilicon hexaphosphide

Covalent compounds may have many or few atoms sharing electrons.

CH4 = methane and C25H52 = candle waxPrefixes are often used before the atom name to indicate the number of atoms in the molecule.

CO = carbon monoxide, CO2 = carbon dioxideWrite the most metallic atom (farthest left) first

Add -ide to theend of the second atom’s name


Comparing Ionic and Covalent Compounds

• To determine whether a compound is ionic or covalent:1. Examine the formula.

• Ionic compounds start with a metal or the ammonium ion.• Covalent compounds start with a non-metal.

2. If the compound is covalent:• Use the prefix system of naming if the compound is binary and does not

start with hydrogen.• If there are more than two different elements, or it starts with H, there is

probably a different, simpler name for the covalent molecule.3. If the compound is ionic:

• Check the metal to see if it is multivalent (add a Roman numeral if it is multivalent). Naming starts with the name of the metal atom.

• If it ends with a single non-metal, naming will just end in -ide.• If it ends in a polyatomic ion, look up the name/formula.

See pages 196 - 197

Take the Section 4.2 Q i


4.3 Balancing Chemical Equations

• Chemical reactions result in chemical changes.Chemical changes occur when new substances are created.The original substance(s), called reactants, change into new substance(s) called products.

• Chemical reactions can be written in different ways.A word equation:

Nitrogen monoxide + oxygen → nitrogen dioxideA symbolic equation:

2NO(g) + O2(g) → 2NO2(g)

See pages 202 - 203

State of matter

- Letters indicate the state of each compound.

(aq) = aqueous/dissolved in water

(s) = solid

( ) = liquid

(g) = gas

Coefficients

- Indicate the ratio of compounds in the reaction.

- Here, there is twice as much NO and NO2 than as is O2.


Conservation of Mass in Chemical Change

• Chemical change means new compounds are created.No new matter is created or destroyed; atoms are just rearranged.All of the matter in the reactants = all of the matter in the products.John Dalton, 200 years ago, realized that atoms simply rearrangethemselves during chemical reactions.Number of each atom in reactants = number of each atom in products.

• The law of conservation of mass:In chemical reactions, atoms are neither created nor destroyed.This law was developed by Antoine and Marie-Anne Lavoisier in the 1700s.Mass of reactants = mass of products

See pages 204 - 205

If you could collect and measure all of the exhaust from this car, you would

find that mass of reactants (gas + O2) = mass of products (exhaust).


Writing and Balancing Chemical Equations

• The simplest form of chemical equation is a word equation.Potassium metal + oxygen gas → potassium oxide

• A skeleton equation shows the formulas of the elements/compounds.A skeleton equation shows atoms, but not quantities of atoms.

K + O2 → K2O• A balanced chemical equation shows all atoms and their quantities

Balancing ensures that the number of each atom is the same on both sides of the reaction arrow.Always use the smallest whole-number ratio.

4K + O2 → 2K2OSee page 206

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Counting Atoms to Balance an Equation

• Using the law of conservation of mass, we can count atoms to balance the number of atoms in chemical equations.

Word equation: methane + oxygen → water + carbon dioxideSkeleton equation: CH4 + O2 → H2O + CO2

To balance the compounds, take note of how many atoms of each element occur on each side of the reaction arrow.

Skeleton equation: CH4 + O2 → H2O + CO2

1 carbon, 4 hydrogen, 2 oxygen → 1 carbon, 2 hydrogen, 3 oxygen

To balance, attempt to find values that equate atoms on both sidesBalanced equation: CH4 + 2O2 → 2H2O + CO2

1 carbon, 4 hydrogen, (2×2) oxygen → 1 carbon, (2×2) hydrogen, (2×1)+2 oxygen

The same number of atoms must be

on each side.

See Page 207(c) McGraw Hill Ryerson 2007

Hints for Writing Word Equations

• Word equations require careful examination to be written correctly.The chemical symbol is used for most elements not in a compound.

Be careful of diatomic and polyatomic elements such as O2, P4 and S8 .The “special seven” are all diatomic elements• H2, N2, O2, F2, Cl2, Br2, I2

See page 208

Several common covalent molecules containing hydrogen have common names that you should know.

For example, methane = CH4, glucose = C6H12O6, ethane = C2H6, ammonia = NH3


Strategies for Balancing Equations

• Balance chemical equations by following these steps:Trial and error will work but can be very inefficient.Balance compounds first and elements last.Balance one compound at a time.Only add coefficients; NEVER change subscripts.If H and O appear in more than one place, attempt to balance them LAST.Polyatomic ions (such as SO4

2–) can often be balanced as a whole group.Always double-check after you think you are finished.

• Balance the following:Fe + Br2 → FeBr3

Sn(NO2)4 + K3PO4 → KNO2 + Sn3 (PO4)4

C2H6 + O2 → CO2 + H2O

See pages 209 - 211Take the Section 4.3 Quiz

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4.1 Atomic Theory and Bonding Atomic Theory - askmryuenaskmryuen.com/askmryuen2007/science10new/BC10_Chapter_4.pdf · 4.1 Atomic Theory and Bonding ... Atomic Theory • Atoms are