Atoms Molecules and Ions by Abhishek Jaguessar

8/4/2019 Atoms Molecules and Ions by Abhishek Jaguessar

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Atoms, Molecules and Ions

By Abhishek Jaguessar


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Daltons Atomic Theory (1808)

1. Elementsare composed of extremely small

particles called atoms. All atoms of a givenelement are identical. The atoms of one elementare different from the atoms of all other elements.

2. Compoundsare composed of atoms of morethan one element. The relative number of atomsof each element in a given compound is alwaysthe same.

3. Chemical reactions only involve the rearrangementof atoms. Atoms are not created or destroyed inchemical reactions.

2.1


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2

2.1


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8 X2Y16 X 8 Y+

2.1


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J.J. Thomson, measured mass/charge of e-

(1906 Nobel Prize in Physics) 2.2


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e-charge = -1.60 x 10-19 C

Thomsons charge/mass of e- = -1.76 x 108 C/g

e-

mass = 9.10 x 10-28

g

Measured mass of e-

(1923 Nobel Prize in Physics)

2.2


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(Uranium compound)2.2


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1. atoms positive charge is concentrated in the nucleus2. proton (p) has opposite (+) charge of electron3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)

particle velocity ~ 1.4 x 107 m/s

(~5% speed of light)

(1908 Nobel Prize in Chemistry)

2.2


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atomic radius ~ 100 pm = 1 x 10-10 m

nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

Rutherfords Model of

the Atom

2.2


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Chadwicks Experiment (1932)

H atoms - 1 p; He atoms - 2 p

mass He/mass H should = 2

measured mass He/mass H = 4

+ 9Be 1n + 12C + energy

neutron (n) is neutral (charge = 0)

n mass ~ p mass = 1.67 x 10-24 g2.2


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Subatomic Particles (Table 2.1)

ParticleMass

(g)Charge

(Coulombs)Charge(units)

Electron (e-) 9.1 x 10

-28-1.6 x 10

-19-1

Proton (p) 1.67 x 10-24

+1.6 x 10-19

+1

Neutron (n) 1.67 x 10-24

0 0

mass p = mass n = 1840 x mass e-2.2


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Atomic number(Z) = number of protons in nucleus

Mass number(A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

Isotopesare atoms of the same element (X) with differentnumbers of neutrons in the nucleus

XAZ

H1

1H (D)2

1H (T)3

1

U23592 U23892

Mass Number

Atomic NumberElement Symbol

2.3


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2.3


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How many protons, neutrons, and electrons are in C146 ?

How many protons, neutrons, and electrons are in C116 ?

6 protons, 8 (14 - 6) neutrons, 6 electrons

6 protons, 5 (11 - 6) neutrons, 6 electrons

Do You Understand Isotopes?

2.3


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Period

G

roup

AlkaliMetal

NobleGas

Halogen

AlkaliEarth

Metal

2.4


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A moleculeis an aggregate of two or more atoms in adefinite arrangement held together by chemical bonds

H2

H2O NH

3CH

4

A diatomic moleculecontains only two atoms

H2, N2, O2, Br2, HCl, CO

A polyatomic moleculecontains more than two atoms

O3, H2O, NH3, CH4

2.5


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An ionis an atom, or group of atoms, that has a netpositive or negative charge.

cation ion with a positive chargeIf a neutral atom loses one or more electronsit becomes a cation.

anion ion with a negative charge

If a neutral atom gains one or more electronsit becomes an anion.

Na 11 protons11 electrons Na+ 11 protons10 electrons

Cl17 protons17 electrons Cl-

17 protons18 electrons

2.5


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A monatomic ioncontains only one atom

A polyatomic ioncontains more than one atom

2.5

Na+, Cl-, Ca2+, O2-, Al3+, N3-

OH-, CN-, NH4

+, NO3

-


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13 protons, 10 (13 3) electrons

34 protons, 36 (34 + 2) electrons

Do You Understand Ions?

2.5

How many protons and electrons are in Al2713 ?3+

How many protons and electrons are in Se78342- ?


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2.5


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2.6


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A molecular formulashows the exact number ofatoms of each element in the smallest unit of a

substance

An empirical formulashows the simplestwhole-number ratio of the atoms in a substance

H2OH2O

molecular empirical

C6H12O6 CH2O

O3 O

N2H4 NH2

2.6


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ionic compoundsconsist of a cation and an anion

the formula is always the same as the empirical formula

the sum of the charges on the cation and anion in eachformula unit must equal zero

The ionic compound NaCl

2.6


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Formula of Ionic Compounds

Al2O3

2.6

2 x +3 = +6 3 x -2 = -6

Al3+ O2-

CaBr2

1 x +2 = +2 2 x -1 = -2

Ca2+ Br-

Na2CO3

1 x +2 = +2 1 x -2 = -2

Na+ CO32-


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Some Polyatomic Ions (Table 2.3)

NH4+

ammonium SO42-

sulfate

CO32-

carbonate SO32-

sulfite

HCO3- bicarbonate NO3- nitrate

ClO3-

chlorate NO2-

nitrite

Cr2O72-

dichromate SCN-

thiocyanate

CrO42-

chromate OH-

hydroxide

2.7


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Chemical Nomenclature

Ionic Compounds often a metal + nonmetal

anion (nonmetal), add ide to element name

BaCl2 barium chloride

K2O potassium oxide

Mg(OH)2 magnesium hydroxide

KNO3 potassium nitrate

2.7


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Transition metal ionic compounds

indicate charge on metal with Roman numerals

FeCl2 2 Cl- -2 so Fe is +2 iron(II) chloride

FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride

Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide

2.7


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Molecular compounds

nonmetals or nonmetals + metalloids

common names

H2O, NH3, CH4, C60

element further left in periodic table is 1st

element closest to bottom of group is 1st

if more than one compound can be formedfrom the same elements, use prefixes to

indicate number of each kind of atom last element ends in ide

2.7


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HI hydrogen iodide

NF3 nitrogen trifluoride

SO2 sulfur dioxide

N2Cl4 dinitrogen tetrachloride

NO2 nitrogen dioxide

N2O dinitrogen monoxide

Molecular Compounds

2.7

TOXIC!

Laughing Gas


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An acidcan be defined as a substance that yieldshydrogen ions (H+) when dissolved in water.

HClPure substance, hydrogen chlorideDissolved in water (H+ Cl-), hydrochloric acid

An oxoacidis an acid that contains hydrogen,oxygen, and another element.

HNO3 nitric acidH2CO3 carbonic acid

H2SO4 sulfuric acid

2.7


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2.7


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A basecan be defined as a substance that yields

hydroxide ions (OH-

) when dissolved in water.

NaOH sodium hydroxide

KOH potassium hydroxide

Ba(OH)2 barium hydroxide

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Atoms Molecules and Ions by Abhishek Jaguessar