Tyas - Atoms, Molecules and Ions 2011

8/3/2019 Tyas - Atoms, Molecules and Ions 2011

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Grade VIII Semester 1

2011/2012

Tyas Ajeng Puspitasari, S.Pd

Junior High School 1 Malang


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To define the meaning of particles of matter (atom, ion and

molecule)

To explain the difference of isotope, isotones and isobar

To explain the difference between the element molecule and the

compound molecule To mention some examples of simple molecules in daily life

To give examples of substances that consist of ions


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On grade VII youve learned that all matters around us are madeup of fundamental matter called ELEMENT.

Element is a simple substance which cannot be broken down into

simpler substance Look at the figure !

A piece of iron is composed of a mass of iron atoms

A piece of iron

Iron atom


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FeDemocrituss model 480 BC

( the father of atomic theory)Fe Fe

Fe Fe

Fe Fe


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Daltons Concept (1808)John Dalton, an English schoolteacher in the early nineteenth

century, combined the idea of elements with the earlier theoryof the atom.

He proposed the following ideas about matter:

(1) Matter is made up of atoms,

(2)Atoms cannot be divided into smaller pieces,(3)All the atoms of an element are exactly alike

(4)Different elements are made of different kinds of atoms.


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Thomsons model 1903 English Physicist, Joseph John

THOMSON describes atoms as likea plum pudding or raisin cake.

The atom was a heavy positivepudding with the light negatively

charged electrons emmbedded in

it ThomsonAtomic

Model


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Rutherfords model 1911 New Zealand Physicist, Ernest

RUTHERFORD describes the nuclearatom

His model of the atom had a tiny,very dense, positively charged

nucleus about 1 /10,000 the diameterof the atom

The very tiny negative electrons

orbited around the nucleus like tinyplanets


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Danish physicist, Niels BOHR, applies his own ideas to the

electrons of the Rutherford atom.

His new model has the electrons in orbit where they areonly able to exist at very definite positions with a very

definite energy (quantised).

This uses quantum theory, which implies that particleshave set amount of energy

Bohrs model 1913


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THE STRUCTURE OF ATOMS

Atoms are made up of three subatomic

particles

Protons carry positive chargeNeutrons having no charge

Electrons carry negative charge

The protons and neutrons are tightly bound together to form

the central portion of an atom called the nucleus.

The electrons are located outside of the nucleus and thought

to move very rapidly throughout a relatively large volume ofspace surrounding the small but very heavy nucleus.


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particles charge Position in atom

Proton

Neutron

electron

+1

No charge

- 1

Atom nucleus

Atom nucleus

Moving around atom

nucleus


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ISOTOPESIsotopes are atoms with the same atomicnumbers but different mass numbers.

EXAMPLES

Hydrogen

Chlorine

Carbon


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ISOBARAtoms of different elements might have

the same mass number.EXAMPLES

ISOTONESAtoms of different elements might have the same number of

neutron

EXAMPLES


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According to Bohr, electrons move around the nucleus infixed orbit or shells

The electron in each shell have different energy level. Theshells closes to the nucleus have lower energy levels than

those farther away

The biggest atoms can have up to 7 electron shells,

However, each shell can contain only a limited number of

electrons. This number depends on their size:1st shell maximum filled with 2 electrons.

2nd shell maximum filled with 8 electrons.

3rd

shell can hold up to 18 electrons, but normally only holdsup to 8 to make atom more stable.

4th shell can hold up to 32 electrons but, like the third shell,normally holds only up to 8 to make atom more stable


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Example of Electron arrangement

Sodiump=11e=11

n=12

Electronic Configuration:

2, 8, 1

1st shell 2nd shell 3rd shell

Electronic Structure

The electron in the outermost shell of an atom

are called the outer electron or valency

electrons

Sodium has 1 valency electron


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When atoms lose or gain electrons, they become

ions

Ion is an atom having electric charge

atom

Loses

electrons+

Positive ion

_ Negative ion

An atom may gain or lose electrons

Gains electrons


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cation ion with a positive charge

If a neutral atom loses one or more electrons it

becomes a cation.

anion ion with a negative charge

If a neutral atom gains one or more electrons itbecomes an anion.

Na11 protons

11 electrons

Na+11 protons

10 electrons

Cl17 protons

17 electrons Cl-17 protons

18 electrons


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Predicting Ionic Charge

Metals tend to form cations (group 1 and 2) Non-metals tend to form anions.(group 5, 6, 7 )

Be2+


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A monatomic ion contains only one atom

Apolyatomic ion contains more than one atom

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

OH-, CN-, NH4+, NO3

-


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A molecule is made up of two or more atoms chemically combined

together.

H2

H2O NH

3CH

4

A diatomic moleculecontains only two atoms

H2, N2, O2, Br2, HCl, CO

Apolyatomic moleculecontains more than two atoms

O3, H2O, NH3, CH4


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Molecules are made up of the same kinds of atoms

Molecules are made up of two or more different kinds of

atoms

Kinds of Molecules


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The using of ions and molecules in chemical product in

daily life

Composer Product

Polyvinyl Chloride (PVC) Water pipe, tile

Polyetilene Carpet, laboratory apparatus

Isoprene (C5H8) andpolystyrene

Rubber

Sucrose (C12H22O11) Sugar, Syrup

Ionic compound NaCl Table saltIon-ion (Cl-, Na+,Mg 3+,

Ca2+)

Isotonic drinks

Documents

Tyas - Atoms, Molecules and Ions 2011