Chapter 2-Structure Atoms and Matter

8/10/2019 Chapter 2-Structure Atoms and Matter

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The Modern Atomic Theory

1. All matter is composed of atoms.The atom is the smallest body

thatretains the unique identityof the element.

2. Atoms of one element cannot be converted into atoms of another

element in a chemical reaction.Elements can only be converted

into other elements in nuclear reactions.

3. All atoms of an element have the same number of protons and

electrons, which determines the chemical behavior of the element.

Isotopes of an element differ in the number of neutrons, and

thus in mass number. A sample of the element is treated asthough its atoms have anaveragemass.

4. Compounds are formed by the chemical combination of two or

more elements in specif ic ratios.


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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-


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Electron- Negatively chargeparticle.

Proton- Positively chargeparticle- The number of protonare equalto thenumber of electronif the atom is neutral.- Proton has opposite sign of an electron- Proton has greater mass than electron.

Neutron- Carries no chargeparticle.- It has almost the ame mass with proton.- The number of neutron is not directly

related to proton or electron.


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General Features of the Atom


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Atom ic 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 different numbersof neutrons in their nuclei

XA

Z

H11 H (D)

21 H (T)

31

U23592 U23892

Mass Number

Atomic NumberElement Symbol


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What are Isotopes?

Isotopes are the elements that have the sameatomic number but the different number of mass.

Hydrogen Deuterium Tritium

H11 H (D)

21 H (T)

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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

Both C are isotopes of carbon. They have the same number of protons

but differ in number of neutrons

Exercise:


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Sample Problem

Determining the Number of Subatomic

Particles in the Isotopes of an Element

PROBLEM:

Silicon(Si) is essential to the computer industry as a majorcomponent of semiconductor chips. It has three naturally occurring

isotopes: 28Si, 29Si, and 30Si. Determine the number of protons,

neutrons, and electrons in each silicon isotope.

PLAN:

We have to use the atomic number and atomic masses.

SOLUTION:

The atomic number of silicon is 14. Therefore

28Si has 14p+, 14e-and 14n0(28-14)

29

Si has 14p+, 14e

-and 15n

0

(29-14)

30Si has 14p+, 14e-and 16n0(30-14)


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The periodic table is a handy tool that correlates the properties of theelements in a systematic way and helps us to make predictions aboutchemical behavior.

Element are arranged by atomic number (shown above the elementsymbol) in horizontal rows called Periodsand vertical columns known as

groupsor families , according to similarities in their chemicals properties

The elements can be divided into three categories- metals, nonmetalsand metalloids

Element are often referred to collectively by their periodic table group

number(Group 1A, Group 2A, and so on).

However, for convenience, some elements groups have been givenspecial names

Group 1A: Alkali metalsGroup 2A: Alkaline earth metals

Group 7A: HalogensGroup 8A: Noble gases, or rare gases


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Period

G

roup

AlkaliMetal

NobleGas

Halogen

AlkaliEarth

Metal


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1. Metallic properties increase. Why?Metals want to lose electrons the farther the electron is from the nucleusthe easier it will be to lose the electron.

2. Radius increases. There is an additional energy level added to each

successive atom.3. Ionization energy decreases. It takes less energy to form an ion.

4. Electronegativity decreases. Electronegativity is the attraction an atomhas for an electron. If the outer shell (valence shell) is farther from the

nucleus there will not be as great attraction if it were closer.5. Oxidation states (charges) remains the samebecause they all have the

same number of electrons in the outer shell and will therefore behave thesame.

6. They all have similar properties.


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1. Metallic properties decrease. As you go from one element to the next thenumber of electrons in the outer shell (valence shell) willincrease. A metal wantsto lose electrons and a nonmetal wants to gain electrons. The more electronspresent in this outer shell the harder it is to lose them all.

2. Radius decreases. All the elements that are on the same periodwill have the same

number of energy levels. The number of protons in the nucleus increases makingthe nuclear charge stonger.It therefore pulls the electrons toward it making theradius smaller as you go from one element to the next.

3. Ionization energy increases. There are more electrons in the outer shell and it istherefore harder to remove them. The electrons are also closer to the nucleus so

there is a greater force holding them there.4. Electronegativity increases. These elements want to gain electrons to complete

their outer shell, so they have a greater force of attraction. Oxidation stateschange (+1, +2, +3, + - 4, -3 , -2, -1)). They all havea different number of electronsin the outer shell.

5. Properties are all different


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Metals, Metalloids, and Nonmetals


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Metals Left-hand side of the table Tendency to lose electrons Conduct heat and electricity Usually solid at room temperature Malleable - can be hammered into different shapes Ductile - can be drawn into wires Luster - they shine

Nonmetals Right-hand side of the table

Tendency to gain electrons Poor conductors of heat or electricity Not malleable or ductile (those that are solids tend to be brittle) Do not exhibit luster

Metalloids (or semimetals)

Mixture of metallic and nonmetallic properties Used for semiconductors


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1A (Group 1) - Alkali metals

They will all form ions with a +1 charge. They all have one selectron in their outer shell. These are very active metals andare seldom found free in nature. As a matter of fact theseelements are not found free in nature.

11A (Group 2)- alkaline earth metals

These are also very active elements, but not as active as thosein group 1. These group 2 elements have properties similar toeach other. They all have two s electrons in their outer shell andwill therefore produce a +2 ion.

111B 11B ( Group 3 12) - Transition elements

These metals are located in the center of the periodic table.They make up groups 3 through 12.


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A moleculeis an aggregate of two or more atoms in a

definite arrangement held together by chemical bonds

H2

H2

O NH3

CH4

A diatom ic mo leculecontains only two atoms

H2, N2, O2, Br2, HCl, CO

A polyatom ic m olecu lecontains more than two atoms

O3, H2O, NH3, CH4


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An ionis an atom, or group of atoms, that has a net

positive or negative charge.

cat ionion with a positive chargeIf a neutral atom losesone or more electrons

it becomes a cation.

anionion with a negative charge

If a neutral atom gainsone or more electronsit becomes an anion.

Na 11 protons11 electrons Na+ 11 protons10 electrons

Cl17 protons

17 electrons Cl-17 protons

18 electrons


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13 protons, 10 (133) electrons

34 protons, 36 (34 + 2) electrons

What are Ions?

How many protons and electrons are in Al2713 ?3+

How many protons and electrons are in Se78342- ?


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A monatom ic ioncontains only one atom

A polyatom ic ioncontains more than one atom

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

OH-, CN-, NH4+, NO3

-


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NH4+

ammonium SO42-

sulfate

CO32-

carbonate SO32-

sulfite

HCO3- bicarbonate NO3- nitrate

ClO3- chlorate NO2

-nitrite

Cr2O72-

dichromate SCN-

thiocyanate

CrO42-

chromate OH- hydroxide


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Chemist use chemical formulas to express the composition in terms of chemical symbols


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A molecular formulashows the exact number of atoms of each

element in the smallest unit of a substance

An empir ical formu lashows the simplest whole-number ratio of

the atoms in a substance

H2OH2O

molecular empirical

C6H12O6 CH2O

O3 O

N2H4 NH2


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An i on ic compoundsconsist of a combination of cations

and an anions

the formula is always the same as the empirical formula

the sum of the charges on the cation(s) and anion(s) in each

formula unit must equal zero

The ionic compound NaCl


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Formula of Ionic Compounds

Al2O3

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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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

Example:


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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

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 formed from the sameelements, use prefixesto indicate number of each kind ofatom

last element ends in ide


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HI hydrogen iodide

NF3 nitrogen trifluoride

SO2 sulfur dioxide

N2Cl4 dinitrogen tetrachloride

NO2 nitrogen dioxide

N2O dinitrogen monoxide

Molecular ompounds

TOXIC


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Sample Problem Naming Binary Molecular Compounds

PROBLEM:

Name the following molecular compound:

PLAN:

(a)SiCI4

SOLUTION:

Use the periodic table to decide which element is the metal and

which the nonmetal. The metal (cation) is named first and weuse the -idesuffix on the nonmetal name root.

(b)iodine and cadmium

(c)strontium and fluorine (d)sulfur and cesium

(a)Silicon Tetrachloride

(b)cadmium iodide

(c)strontium fluoride

(d)cesium sulfide


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An acidcan be defined as a substance that yields

hydrogen ions (H+) when dissolved in water.

HClPure substance, hydrogen chloride

Dissolved in water (H+Cl-), hydrochloric acid

All acids begin with H.

Two types of acids:

Oxyacids

Non-oxyacids (axoanion)


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oxo id

An oxoacidis an acid that contains hydrogen,

oxygen, and another element (The central element).

Usually written with the H first, followed by the central

elementand thenO, as illustrated by the followingexample :

HNO3 nitric acid

H2CO3 carbonic acid

H2SO4 sulfuric acid

HCIO3 chloric acid


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Addition of one O atom to the -ic acid: the acid calledper-ic acid. Thus Adding an O atomto HCIO3 changeschloric acid to perchloric acid (HCIO4)

Removal of one O atom to the -ic acid: the acid called -ous acid. Thus Removal of one O atomto HNO3changes nitricacid to nitrous acid (HNO2)

Removal of two O atom to the -ic acid: the acid called hypo-ous acid. Thus when Removal of two O atomto HBrO3changes to hypobromous acid (HBrO)


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When all the H ions was removed from -ic acid, the anionsname ends with -ate.

Example:

Chloric acid (HCIO3 ) changes to carbonate (CIO3)

When all the H atoms from the -ous acid, the anions nameends with -ite.

Example:(HCIO2) changes to chlorite(CIO2 )

-


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Oxoacid names are similar to those of the oxoanions, except for two suffix

changes:

Anion -ate suffix becomes an -ic suffix in the acid. Anion -ite suffix

becomes an -ous suffix in the acid. The oxoanion prefixes hypo- and per- are retained.

Example :

Thus, BrO4- isperbromate, and HBrO4isperbromicacid; IO2-is iodite, andHIO2is iodousacid.

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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Chapter 2-Structure Atoms and Matter