Atoms, Molecules & Ions

AP ChemistryChapter 2.1

(Days 3 & 4)

Subatomic Particles

• Protons and electrons are the only particles that have a charge.

• Protons and neutrons have essentially the same mass.

• The mass of an electron is so small we ignore it.

Symbols of Elements

Elements are symbolized by one or two letters.

Atomic Number

All atoms of the same element have the same number of protons: The atomic number (Z)

In a neutral atom, the # of p+ = the # of e-

Atomic Mass

The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom. Remember, electron mass is so tiny we essentially ignore it.

Isotopes

• Atoms of the same element with different masses.

• Isotopes have different numbers of neutrons.

116C

126C

136C

146C

How many neutrons are there in an atom of 14C?

1. 62. 83. 124. 14

Correct Answer:

Atomic numberMass number 14

6 CThe difference between the mass number and the atomic number is the number of neutrons (14 6) = 8.

1.6

2.8

3.12

4.14

Determining the Number of Subatomic Particles in Atoms

How many protons, neutrons, and electrons are in (a) an atom of 197Au (b) an atom of strontium-90?

Determining the Number of Subatomic Particles in Atoms

How many protons, neutrons, and electrons are in (a) a 138Ba atom, (b) an atom of phosphorus-31?

Answer: (a) 56 protons, 56 electrons, and 82 neutrons; (b) 15 protons, 15 electrons, and 16 neutrons.

Periodic Table

• A systematic catalog of elements.

• Elements are arranged in order of atomic number.

Periodicity

When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities.

Periodic Table

• The rows on the periodic chart are periods or series.

• Columns are groups or families.

• Elements in the same group have similar chemical properties.

Groups

These five groups are known by their names.

Solids, Liquids, & Gases

Metals, Nonmetals, SemimetalsMetals – good conductors, high luster, ductile, malleable

Metals, Nonmetals, SemimetalsNonmetals – most are gases, poor conductors, brittle

Metals, Nonmetals, SemimetalsSemi-metals (metalloids) – have properties similar to metals and nonmetals

Diatomic Molecules

These seven elements occur naturally as molecules containing two atoms:

• Hydrogen & draw a 7 starting at N (element 7)• Hockey stick & puck• BrINClHOF (Brinklehoff)• I Have No Bright Or Clever Friends

Compounds and Chemical Formulas

• Molecule - A single particle, contains two or more nonmetal atoms; covalently bonded

• Formula Unit – a particle containing a metal with a nonmetal; ionicly bonded

• Chemical formulas – give the number of atoms of each element in a compound

Identifying Ionic and Molecular Compounds

Which of the following compounds would you expect to be ionic: N2O, Na2O, CaCl2, SF4?

Which of the following compounds are molecular: CBr4, FeS, P4 O6, PbF2 ?

Answer: CBr4 and P4 O6

Identifying Ionic and Molecular CompoundsWhich of the following compounds are molecular: CBr4, FeS, P4 O6, PbF2 ?

Answer: CBr4 and P4 O6

Which combination is likely to produce an ionic compound?

• C and H• S and Cl• Ca and F• Br and I• Xe and F

Which combination is likely to produce an ionic compound?

• C and H• S and Cl• Ca and F• Br and I• Xe and F

• Chemical formulas – give the number of atoms of each element in a compound

Compounds and Chemical Formulas

Compounds and Chemical Formulas

State the composition for a molecule of trinitrotoluene, TNT: C7H5(NO2)3

•7 carbon atoms, 5 hydrogen atoms, 3 nitrogen atoms, 6 oxygen atoms; 21 atoms total

Types of Formulas

• Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound.

• Molecular formulas give the exact number of atoms of each element in a compound.

• Sometimes they can be the same

Relating Empirical and Molecular FormulasWrite the empirical formulas for the following molecules: (a) glucose, a substance also known as either blood sugar or dextrose, whose molecular formula is C6H12O6; (b) nitrous oxide, a substance used as an anesthetic and commonly called laughing gas, whose molecular formula is N2O.

Give the empirical formula for the substance called diborane, whose molecular formula is B2H6.

Answer:  BH3

Relating Empirical and Molecular FormulasGive the empirical formula for the substance called diborane, whose molecular formula is B2H6.

Answer:  BH3

a. C2H6

b. CH3

Ions

• When atoms lose or gain electrons, they become ions.

Ions• Cation – positive ion

– Has the “t” like a + sign– Formed by metals and some nonmetals– Lost electrons– #p+ > #e-

• Anion – negative ion– Gained electrons– Formed by nonmetals– #p+ < #e-

• Polyatomic ions– Made up of two or more atoms– Can be positive or negative

An isotope of Cr3+ ion containing 24 protons and 27 neutrons would contain ___ electrons.

1. 21

2. 24

3. 27

4. 3

Correct Answer:

The +3 charge indicates there are 3 more protons than electrons:

24 3 = 21

1. 21

2. 24

3. 27

4. 3

Which of the following species has the greatest number of electrons?

1. Cl

• Ca2+

• P3

• K• Ar

Correct Answer:

K has 19 electrons; all the other species listed have only 18 electrons.

1. Cl

• Ca2+

• P3

• K• Ar

Writing Chemical Symbols for Ions

Give the chemical symbol, including mass number, for each of the following ions: (a) The ion with 22 protons, 26 neutrons, and 19 electrons; (b) the ion of sulfur that has 16 neutrons and 18 electrons.

Solution (a) The symbol for the ion is 48Ti3+.(b) The symbol for the ion is 32S2–.

Writing Chemical Symbols for Ions

How many protons and electrons does the Se2– ion possess?

Answer: 34 protons and 36 electrons

IsoelectronicAtoms and ions are considered

isoelectronic when they have the same number of electrons.

1224Mg

714N 3

1327Al3

1020Ne

919F

Which of the following are isoelectronic?

714N 3

1020Ne

1327Al3

5.

1.

2.

3.

4.

1020Ne

919F

1224Mg

1020Ne

1327Al3

1020Ne

919F

None of the above

Which of the following are isoelectronic?

714N 3

1020Ne

1327Al3

5.

1.

2.

3.

4.

1020Ne

919F

1224Mg

1020Ne

1327Al3

1020Ne

919F

None of the above

Group 1A = 1+

Group 2A = 2+

Group 3A = 3+

Group 5A = 3–

Group 6A = 2–

Group 7A = 1–

Group 4A = varies

Monoatomic Ions

• Transition metals form more than one cation

The Stock System• Iron can be Fe2+ or Fe3+

• Iron (II) ion, iron (III) ion• Cu+ and Cu2+

Polyatomic Ions• Polyatomic anions usually contain one

or more elements combined with oxygen

• Most end in “-ate”• Those that end in “-ite” have one less

oxygen than “-ate”• Exceptions include

– CN1-, cyanide– OH1-, hydroxide– O2

2-, peroxide– NH4

1+, ammonium

Patterns in Oxyanion Nomenclature

• When there are two oxyanions involving the same element:– The one with fewer oxygens ends in -ite

• NO2− : nitrite; SO3

2− : sulfite

– The one with more oxygens ends in -ate• NO3

− : nitrate; SO42− : sulfate

Writing Chemical Formulas• A formula unit is the simplest

representative particle in an ionic compound

• A formula unit is neutral• Positive and negative charges

must cancel out (cation + anion)• Made between a metal & a

nonmetal

Naming Formula units

• The metal is written first followed by the nonmetal

• The metal keeps its name, the nonmetal gets the suffix “-ide”

MgO

Al2O3

CaS

NaCl

K3N

sodium chloridealuminum oxide

calcium sulfide

magnesium oxide

potassium nitride

Formula units from names

• All formula units have a neutral charge

• The + and the – must = zero• Beryllium fluoride• Potassium chloride• Strontium nitride

The correct name for the compound, MgC2 is

1. Carbon magneside2. Magnesium carbide3. Magnesium carbonate4. Manganese dicarbide5. Magnesium dicarbide

Correct Answer:

In this unusual ionic compound, the cation is magnesium cation (Mg2+) and the anion is carbide or acetylide (C2

2).

1. Carbon magneside2. Magnesium carbide3. Magnesium carbonate4. Manganese dicarbide5. Magnesium dicarbide

The simplest chemical formula for the binary ionic compound CaxNy is

1. Ca2N2. Ca2N3

3. Ca3N2

4. Ca3N

Correct Answer:

Ca loses two electrons to become Ca2+, while N gains three electrons to become N3

. To be neutral, positive charges and negative charges have to balance.

1. Ca2N2. Ca2N3

3. Ca3N2

4. Ca3N

Transition metals in formula units

• Transition metals have multiple oxidation numbers (aka charges)

• Exceptions: Ag+ Cd2+ Zn2+

• Must figure out charges from name or formula

• iron (II) oxide

• CuCl2

Naming with polyatomics• Polyatomics end mostly in “-ate” and “-ite”

– Exceptions: ammonium (NH4+), hydroxide (OH-),

cyanide (CN-), & peroxide (O2-2)

• A formula with a polyatomic will have 3 or more different elements.

• Only one positive polyatomic: NH4+

ammonium

• Ca(NO3)2

• K2SO4

• aluminum acetate• sodium phosphate

The compound, CuSO4, is called

1. Copper sulfate2. Copper (II) sulfide3. Copper (I) sulfite4. Copper (I) sulfate5. Copper (II)

sulfate

Correct Answer:

The compound is ionic, derived from the copper(II) cation (Cu2+) and the sulfate anion (SO4

2).

1. Copper sulfate2. Copper (II)

sulfide3. Copper (I) sulfite4. Copper (I)

sulfate5. Copper (II)

sulfate

Using Ionic Charge to Write Empirical Formulas for Ionic Compounds

What are the empirical formulas of the compounds formed by (a) Al3+ and Cl– ions, (b) Al3+ and O2 – ions, (c) Mg2+ and NO3

– ions?

(a) The formula is AlCl3.(b) The formula is Al2O3.(c) The formula is Mg(NO3)2.

Using Ionic Charge to Write Empirical Formulas for Ionic Compounds

Write the empirical formulas for the compounds formed by the following ions: (a) Na+ and PO4

3– , (b) Zn2+ and SO42– , (c)

Fe3+ and CO32–.

Answers: (a) Na3PO4, (b) ZnSO4, (c) Fe2(CO3)3

Determining the Names of Ionic Compounds from Their Formulas

Name the following compounds: (a) K2SO4 , (b) Ba(OH)2 , (c) FeCl3.

(a) potassium sulfate (b) barium hydroxide(c) Iron (III) chloride

Determining the Names of Ionic Compounds from Their Formulas

Name the following compounds: (a) NH4Br, (b) Cr2O3, (c) Ca(NO3)2.

Answers: (a) ammonium bromide, (b) chromium(III) oxide, (c) cobalt(II) nitrate

Determining the Formulas of Ionic Compounds from Their Names

Write the chemical formulas for the following compounds: (a) potassium sulfide, (b) calcium hydrogen carbonate, (c) nickel(II) perchlorate.

(a) K2S (b) Ca(HCO3)2

(c) Ni(ClO4)2.

Determining the Formulas of Ionic Compounds from Their Names

Give the chemical formula for (a) magnesium sulfate, (b) silver sulfide, (c) lead(II) nitrate.

Answers: (a) MgSO4 , (b) Ag2S, (c) Pb(NO3)2

Nomenclature of Binary Molecular Compounds

• The less electronegative atom is usually listed first.

• A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however.)

Nomenclature of Binary Molecular Compounds

• The ending on the more electronegative element is changed to -ide.

– CO2: carbon dioxide– CCl4: carbon

tetrachloride

Nomenclature of Binary Compounds

If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one:

N2O5: dinitrogen pentoxide

Molecular formulas

• NO2

• P4S10

• NI3• Cl2O

• CO• Xenon hexafluoride• Diphosphorus pentaoxide

Elements by themselves

• Solo elements are always just named for themselves no matter how many there are

• N2

• S8

• Fe

The molecular compound N2O4 is named:

1. Nitrogen oxide2. Oxygen nitride3. Dinitrogen

quartoxide4. Dinitrogen tetroxide5. Nitrous oxide

Correct Answer:

Remember: the vowel “A” on the prefix tetra- is dropped because oxide starts with the vowel “O.”

1. Nitrogen oxide2. Oxygen nitride3. Dinitrogen

quartoxide4. Dinitrogen tetroxide5. Nitrous oxide

Relating the Names and Formulas of Binary Molecular CompoundsName the following compounds: (a) SO2, (b) PCl5, (c) N2O3.

(a) sulfur dioxide, (b) phosphorus pentachloride, and (c) dinitrogen trioxide.

Relating the Names and Formulas of Binary Molecular Compounds

Give the chemical formula for (a) silicon tetrabromide, (b) disulfur dichloride.

Answers: (a) SiBr4, (b) S2Cl2

Relating the Names and Formulas of AcidsName the following acids: (a) HCN, (b) HNO3, (c) H2SO4, (d) H2SO3.

(a) hydrocyanic acid (b) nitric acid (c) sulfuric acid. (d) sulfurous acid

Relating the Names and Formulas of AcidsGive the chemical formulas for (a) hydrobromic acid, (b) carbonic acid.

Answers: (a) HBr, (b) H2CO3

Acid Nomenclature

• If the anion in the acid ends in -ide, change the ending to -ic acid and add the prefix hydro- :– HCl: hydrochloric

acid– HBr: hydrobromic

acid– HI: hydroiodic acid

Acid Nomenclature

• If the anion in the acid ends in -ite, change the ending to -ous acid:– HClO: hypochlorous

acid

– HClO2: chlorous acid

Acid Nomenclature

• If the anion in the acid ends in -ate, change the ending to -ic acid:– HClO3: chloric acid

– HClO4: perchloric acid

The acid HClO3 is known as:

ClO

O

HO1. Perchloric acid2. Chloric acid3. Chlorous acid4. Hypochlorous acid5. Hydrochloric acid

The acid HClO3 is known as:

ClO

O

HO1. Perchloric acid2. Chloric acid3. Chlorous acid4. Hypochlorous acid5. Hydrochloric acid

Simple Organic Chemistry and Hydrocarbons

• Hydrocarbons contain only two elements: 1) hydrogen, & 2) carbon– simplest hydrocarbons called

“alkanes”, which contain only carbon to carbon single covalent bonds (CnH2n+2)

– methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas

Simple Organic Chemistry and Hydrocarbons

1. meth- many2. eth- elephants3. prop- pee4. but- by5. pent- plants

6. hex-7. hept-8. oct-9. non-10.dec-

Alcohols•Alcohols - a class of organic

compounds with an -OH group–The -OH functional group in alcohols is called a “hydroxyl” group; thus R-OH is the formula

•How is this different from the hydroxide ion? (covalent bonding with the carbon- not ionic with a metal like bases)

Alcohols•For IUPAC naming:

–drop the -e ending of the parent alkane name; add ending of -ol, number the position of –OH

–The hydroxyl is given the lowest position number (1-propanol, 2-propanol)

Properties of Alcohols

• Many aliphatic alcohols used in laboratories, clinics, and industry– Isopropyl alcohol (2-propanol) is rubbing alcohol; used as antiseptic, and a base for perfume, creams, lotions, and other cosmetics

Properties of Alcohols

•Ethyl alcohol (ethanol) used in the intoxicating beverages; also an important industrial solvent

Writing Structural and Molecular Formulas for Hydrocarbons

Consider the alkane called pentane. (a) Assuming that the carbon atoms are in a straight line, write a structural formula for pentane. (b) What is the molecular formula for pentane?

C5H12

Writing Structural and Molecular Formulas for Hydrocarbons

Butane is the alkane with four carbon atoms. (a) What is the molecular formula of butane? (b) What are the name and molecular formula of an alcohol derived from butane?

Answers: (a) C4H10 , (b) butanol, C4H10O or C4H9OH