Atom, Molecule, Ion and Periodic Table

8/11/2019 Atom, Molecule, Ion and Periodic Table

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Atoms, Molecules and Ions


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ATOMS


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Daltons Atomic Theory (1808)

1. Each element is made up of tiny particles called atoms.

2. All atomsof a given element are identical, having the

same size, mass and chemical properties. The atoms of

one element are different from the atoms of all other

elements.

3. Compounds are formed when atoms of different

elements combine with each other. A given compound

always has same relative numbers and types of atoms.

4. A chemical react ioninvolves reorganization of theatoms-changes in the way they are bound together. The

atoms themselves are not changes in a chemical

reactions.


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2.1

Daltons Atomic Theory


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8 X2Y16 X 8 Y+


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Cathode Ray Tube


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Cathode Ray Tube


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Thompsons Model of Atom

(Plum Pudding Model)

Spherical cloud of

positive charge

electron


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1. atoms positive charge is concentrated in the nucleus

2. proton (p) has opposite (+) charge of electron (-)

particle velocity ~ 1.4 x 107m/s

(~5% speed of light)

(1908 Nobel Prize in Chemistry)


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(a)

(b)

(a) The expected results of the metal foil experiment if Thompsons model

were correct

(b) Actual results


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e-charge = -1.60 x 10-19C

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

e-

mass = 9.10 x 10-28

g

Measured mass of e-

(1923 Nobel Prize in Physics)


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mass p = mass n = 1840 x mass e-

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.


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Atomic number(Z) = number of protons or electrons

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

= atomic number (Z) + number of neutrons

Isotopesare atoms of the same element (X) with different

numbers of neutrons in their nuclei

XAZ

H11 H (D)

21 H (T)

31

U

235

92 U

238

92

Mass Number

Atomic NumberElement Symbol

Atomic number, Mass number and Isotopes


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

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

Do You Understand Isotopes?

How many protons, neutrons, and electrons are in C14

6 ?

How many protons, neutrons, and electrons are in C11

6 ?


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PERIODIC TABLE


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PERIODIC TABLE

A systematic catalog of

elements.

Elements are arranged in

order of atomic number. The rows on the periodic

chart are periods.

Columns are groups.

Elements in the same grouphave similar chemical

properties.


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Groups

These five groups are commonly referred to by

these names


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Period

Group

AlkaliMetal

NobleG

as

Halo

gen

AlkaliEarth

Metal

Transition metals


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MOLECULE & ION


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A moleculeis an aggregate of two or more atoms in a

definite arrangement held together by chemical forces

H2

H2

O NH3

CH4

A diatom ic molecu lecontains 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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Ions

When atoms lose or gain electrons, they become

ions.

Cations are positive and are formed by elements on the

left side of the periodic chart.

Anions are negative and are formed by elements on the

right side of the periodic chart.


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Ionic Bonds

Ionic compounds (such as NaCl) are generally

formed between metals and nonmetals.


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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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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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13 protons, 10 (133) electrons

34 protons, 36 (34 + 2) electrons

Do You Understand Ions?

How many protons and electrons are in ?Al2713

3+

How many protons and electrons are in ?Se7834

2-


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2.6


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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 formulashows the simplest

whole-number ratio of the atoms in a substance

H2OH2O

molecular empirical

C6H12O6 CH2O

O3 O

N2H4 NH2


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Structural formulas show the

order in which atoms arebonded.

Perspective drawings also show

the three-dimensional array of

atoms in a compound.


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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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Writing Formulas

Because compounds are electrically neutral, one

can determine the formula of a compound thisway:

The charge on the cation becomes the subscript on the

anion.

The charge on the anion becomes the subscript on thecation.

If these subscripts are not in the lowest whole-number

ratio, divide them by the greatest common factor.


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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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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


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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


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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

formed from the same elements, use

prefixes to indicate number of each

kind of atom

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 Compounds

TOXIC!

LaughingGas


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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

An oxoacidis an acid that contains hydrogen,

oxygen, and another element.

HNO3 nitric acid

H2CO3 carbonic acid

H2SO4 sulfuric acid

HNO3


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2.7

N l t f Bi


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Nomenclature of Binary

Compounds

The less electronegativeatom is usually listed first.

A prefix is used to denotethe number of atoms ofeach element in thecompound (mono- is notused on the first element

listed, however.)

N l t f Bi


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Nomenclature of Binary

Compounds

The ending on the more

electronegative element is

changed to -ide.

CO2: carbon dioxide

CCl4: carbon tetrachloride


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Nomenclature of Binary Compounds

If the prefix ends with aoroand the name of theelement begins with a

vowel, the two successivevowels are often elided intoone:

N2O5: dinitrogen pentoxide

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Atom, Molecule, Ion and Periodic Table

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