7/30/2019 Madhav Makkar 2007

1/27

Chemistry and Engineering

Tinier stuff (Particle Physics)

Protons, Neutrons, Electrons

Atoms

Molecules

Big stuff (objects, etc.)

Materials

1

7/30/2019 Madhav Makkar 2007

2/27

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

2

7/30/2019 Madhav Makkar 2007

3/27

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

7/30/2019 Madhav Makkar 2007

4/27

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

7/30/2019 Madhav Makkar 2007

5/27

ATOMIC STRUCTURE

7/30/2019 Madhav Makkar 2007

6/27

ATOMIC STRUCTURE

7/30/2019 Madhav Makkar 2007

7/27

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

7/30/2019 Madhav Makkar 2007

8/27

Atoms

Sub-atomic particles

Electrons Protons

Neutrons

7/30/2019 Madhav Makkar 2007

9/27

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

7/30/2019 Madhav Makkar 2007

10/27

ELECTRONS

Small negatively charged particle

Orbit, circle, around the nucleus

Have no mass. Atoms are neutral.

Number of electrons = number of protons

7/30/2019 Madhav Makkar 2007

11/27

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

7/30/2019 Madhav Makkar 2007

12/27

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

7/30/2019 Madhav Makkar 2007

13/27

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

7/30/2019 Madhav Makkar 2007

14/27

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

7/30/2019 Madhav Makkar 2007

15/27

What's a molecule?

Definition:

The smallest particles of an element or

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

7/30/2019 Madhav Makkar 2007

16/27

EXAMPLES OF MOLECULES

7/30/2019 Madhav Makkar 2007

17/27

Examples of molecules

7/30/2019 Madhav Makkar 2007

18/27

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.

7/30/2019 Madhav Makkar 2007

19/27

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.

7/30/2019 Madhav Makkar 2007

20/27

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

7/30/2019 Madhav Makkar 2007

21/27

7/30/2019 Madhav Makkar 2007

22/27

Pure substances

7/30/2019 Madhav Makkar 2007

23/27

7/30/2019 Madhav Makkar 2007

24/27

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

7/30/2019 Madhav Makkar 2007

25/27

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

7/30/2019 Madhav Makkar 2007

26/27

DNA

7/30/2019 Madhav Makkar 2007

27/27

NAME:- MADHAV MAKKAR

CLASS:- 9thD

ROLL No. 10

Project on Atoms & Molecules

Submitted to:-

ANJU AHUJA MAM