Download - Madhav Makkar 2007

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Chemistry and Engineering

Tinier stuff (Particle Physics)

Protons, Neutrons, Electrons

Atoms

Molecules

Big stuff (objects, etc.)

Materials

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Advice

If you are worried about chemistry, dontget behind! Keep up with reading,homework etc

If I seem to think you know more than

you really do, let me know Get help if you need it (classmates, TA`s,

me..)

Focus on understanding, not just on

guessing what might be on exams

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What's an atom?Definition:

A microscopic small particle that could not be madeany smaller and still behave as a chemical system.Atoms are the smallest particles that can exist and

represent elements identity. Atoms cannot be created

or destroyed


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Atoms

Atoms consist of protons, neutrons,electrons

The atomic structure is shown in thediagram below

Protons have positive charge Electrons have negative charge

Neutrons have no charge


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ATOMIC STRUCTURE


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ATOMIC STRUCTURE


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Properties

Particle Mass (kg) Mass (amu)# Charge*Electron 9.10939 x 10 -31 0.00055 = 0 - 1Proton 1.67262 x 10 -27 1.00728 = 1 +1Neutron 1.67493 x 10 -27 1.00866 = 1 0


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Atoms

Sub-atomic particles

Electrons Protons

Neutrons


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ATOMIC PARTICLES: Atoms consist of three subatomic particles: electrons

electrons are negatively charged particles andtheir properties are summarized in the followingtable

protonsprotons are positively charged particles and their

properties are summarized in the following table

neutronsneutrons have no charge and their properties are

summarized in the following table


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ELECTRONS

Small negatively charged particle

Orbit, circle, around the nucleus

Have no mass. Atoms are neutral.

Number of electrons = number of protons


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PROTONS:

small, positively charged particles

reside in the nucleus

along with the neutron, make up most ofthe mass of the atom

the number of protons is what defines

the type of a particular atom. Atoms are neutral

Number of protons = number of electrons


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NEUTRONS:

small particles with no charge

reside in the nucleus

along with the proton, make up most ofthe mass of the atom

a differing number of neutrons is what

defines an "isotope"of an atom


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ATOMS--Dalton's Atomic Theory

All matter (including elements) iscomposed of atoms; each atom is a very

small, chemically indivisible particle the word 'atom' is from the Greek word"atmos" which means "cannot be cut apart"

elements are different because they are

composed of different types of atoms each type of atom has properties different

from other atoms


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Atomic theory of matter

Matter composed of atoms

Atoms of given element have identical

properties Different elements have different

properties

Atoms combine in whole number ratios Not created or destroyed in ordinary

chemical reactions


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What's a molecule?

Definition:

The smallest particles of an element or

compound that can exist and retain thechemical properties of that element orcompound


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EXAMPLES OF MOLECULES


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Examples of molecules


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AtomicityThe atoms of the noble gases, Helium, Neon,Mercury vapour can all exist on their own.These are said to be monatomic substances-the atom and the molecule being the sameOn the other hand oxygen, nitrogen,hydrogen, chlorine are diatomic and hence

their formula are: 02, N2, H2, Cl2. there are afew well-known cases of higher atomicity, suchare ozone O3 and white phosphorus P4. in thissense the molecule is also the smallest particleof a compound that can exist in the free state.Definition:- the atomicity of a substancewhether an element or a compound is thenumber of atoms in one molecule.


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Compounds

Only few elements are found free in nature: e.g.carbon, nitrogen , oxygen, sulphur, the noble

gases, copper and gold.Most elements are found as compounds.Compounds are formed by two or more elementscombining together millions of compounds areknown and carbon is the element that forms the

most.Definition: a compound is a substance whichcontains two or more elements combined in such away their properties are changerMolecules: atoms of an element may not be able

to exist singly: the atomicity of an element is thenumber if the atoms in on moleculeDefinition: the molecule is the smallest particle ofan element which can exist in the free state underordinary conditions.


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Mixtures

A pure substance is one in which all the

molecule alike. Element and compounds arethe only pure substances that can exist. Iftwo or more kinds of molecules are presenttogether they form a mixture. Most of the

materials encountered are mixtures: air,earth, sea water, plants.

Definition: a mixture contains two or moredifferent substances either elements orcompounds, which are not chemically joinedtogether


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Pure substances


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ATOMIC MASS NUMBER

the mass number has the symbol, A,and is shown as a subscript to theelement symbol

the mass number gives the mass ofatom in amu, atomic mass number, andis approximately equal to the number ofprotons plus the number of neutrons


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Law of constant composition

Reactions take place between wholenumbers of atoms at constant proportion

chemical reactions rearrange the atomsby rearranging the atoms and their ratios of

chemical combination, the substances change chemical reactions cannot create or

destroy matter, they can only rearrangeit, therefore all atoms in a chemical

reaction product, must have occurredwithin the reactants


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DNA


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NAME:- MADHAV MAKKAR

CLASS:- 9thD

ROLL No. 10

Project on Atoms & Molecules

Submitted to:-

ANJU AHUJA MAM