ACHM 111,Week 2 Atoms and Molecules

7/29/2019 ACHM 111,Week 2 Atoms and Molecules

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General information


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Dr. Kyriacos Kyriacou

Biochemistry, BSc, UK, 1977

Biochemistry, PhD, UK, 1982

Spent 15 years in UK

At Frederick since 1991

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Chemistry ACHM 111

4 ECTS , lecture and lab

Lecture once a week

Group 1: Mondays 6:00-9:30 PM

Group 2: Tuesdays 6:00-9:30 PM

Laboratory: Later in the course

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Chemistry ACHM111

Course assessment

Course work 40%:i. 20% Mid Term Exams

ii. 10% Laboratory work

iii. 10% Quiz

Final Exam 60%

Total: 100%

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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, dont get

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 guessingwhat might be on exams

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Atoms and molecules

ACHM 111


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Particles

Atoms

molecules


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What's an atom?

Definition:A microscopic small particle that could not

be made any smaller and still behave as a

chemical system. Atoms are the smallestparticles 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 the diagram

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 - 1

Proton 1.67262 x 10 -27 1.00728 = 1 +1

Neutron 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 and their

properties are summarized in the following table protons

protons are positively charged particles and theirproperties are summarized in the following table

neutrons neutrons 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 of themass 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 of themass 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) is composed ofatoms; each atom is a very small, chemicallyindivisible particle

the word 'atom' is from the Greek word "atmos"which means "cannot be cut apart"

elements are different because they arecomposed of different types of atoms

each type of atom has properties differentfrom 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 chemicalreactions


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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 or

compound


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Molecules

Molecular formula gives composition:

number of atoms of each element

present

Molecular mass= sum of masses of

atoms


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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, Mercuryvapour can all exist on their own. These are said to be

monatomic substances- the atom and the moleculebeing the same

On the other hand oxygen, nitrogen, hydrogen,chlorine are diatomic and hence their formula are: 0

2

,N2, H2, Cl2. there are a few well-known cases of higheratomicity, such are ozone O3 and white phosphorus P4.in this sense the molecule is also the smallest particleof a compound that can exist in the free state.

Definition: the atomicity of a substance whether anelement or a compound is the number of atoms in onemolecule.


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Representing molecules

Names: ethanol, ethyl alcohol

Formulas: C2H8O, C2H5OH, CH3CH2OH

Structural drawings

Models


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Formula


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Matter - particles

Matter Elements, compounds, mixtures

Elements can be made from atoms or

molecules

Compounds can be made only from molecules

Mixtures can be made from either atoms or

molecules.


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Atomic and molecular structure

All matter living or dead consists of materials. Innature their are 116 fundamental materials these arecalled elements.

Definition: an element is a substance that cannot besplit up into two or more substances by chemical

means.Elements may be: a. Solid-iron, carbon

b. liquids- mercury, bromine

c. gases- oxygen, hydrogen

The elements are all composed of particles smallerthan atoms known as electrons, protons and neutrons

Compounds


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CompoundsOnly 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 elements combining together millions of

compounds are known and carbon is the element that forms the

most.

Definition: a compound is a substance which contains two or

more elements combined in such a way their properties are

changer

Molecules: atoms of an element may not be able to exist singly:

the atomicity of an element is the number if the atoms in on

molecule

Definition: the molecule is the smallest particle of an element

which can exist in the free state under ordinary conditions.


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Compounds

compounds are composed of two or more

atoms chemically combined in fixed

proportions

for example, water, H2O, always occurs in a ratio of

2 hydrogens : 1 oxygen

if the ratio were anything else it would not be

water, H2O2 with a ratio of 2 : 2 is peroxide,certainly not water


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Mixtures

A pure substance is one in which all the molecule alike.

Element and compounds are the only pure substancesthat can exist. If two or more kinds of molecules are

present together they form a mixture. Most of the

materials encountered are mixtures: air, earth, sea

water, plants. One of the chemicals most important anddifficulty jobs is to sort out the naturally occurring

mixtures into their pure components in order to

characterize them.

Definition: a mixture contains two or more different

substances either elements or compounds, which are

not chemically joined together


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Mixtures and compoundsMixtures and compounds both contain more than oneelement and so should be separable into their componentelements. This process may be easy or difficult but it isnot the only criterion for deciding whether a givenmaterial is a mixture or a compound.

Example: consider two elements iron and sulphur

Iron form of fillingsSulphur- form of yellow powder

Mix them together without heat mixture

Heat mixture in a test tube

This process of water of crystallization in a substance e.g.copper sulphate -5- water does not make it a mixturebecause the composition is fixed.


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Pure substances


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Element, Atom, Compound, Molecule

An element is a substance which contains only one kind ofatom: lead (Pb), silver (Ag), hydrogen (H2), oxygen (O2).

An atom is the smallest particle of an element which exhibits thephysical and chemical characteristics of that element.

A compound is a substance which contains two or more kinds ofatoms: carbon dioxide (CO2), calcium oxide (CaO), sodiumhydroxide (NaOH).

A molecule is the smallest particle of a substance which exhibits thephysical and chemical characteristics of that substance.

Monoatomic molecules of elements - Cu, Ag, Na, etc. Multiatomic molecules of elements - H2, N2, O2, F2, Cl2, Br2, I2, P4,

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Molecules of compounds - Na2O, KOH, CaSO4, HBr, H2CO3


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Atomic structure

Rutherford developed the "nuclear" model of the atom based upon his experiment which showed that atoms contain

regions of highly dense, positive material, called the nucleus

the nucleus is verydense, 99.95% (or more) of the mass of theatom is in the nucleuswhich has a diameter of approximately 10

-15 m--a matchbox of nucleus material would weigh 2 billiontons! The density is approximately 1013 - 1014 g/cm3.

Rutherford discovered this through his famous experiment withgold foil in which he shot alpha particles (fairly massive particleswith a positive charge) through thin gold foil and found thatmany particles were strongly deflected and some bounced back

at him! This could only happen if the gold foil atoms containedmassive centers that had a positive charge, as exhibited in thefigure below.


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Atomic structure


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Atoms characteristics

Atomic number identity of atom. Most

important.

Determined by number of protons

Atomic mass number

Sum of number protons plus number of neutrons


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ATOMIC NUMBER:

the atomic number has the symbol, Z, and isshown as a superscript to the element symbol

the atomic number gives the number of protonsin the nucleus (and the number of electrons if thespecies is neutral) of a particular atom

the atomic number defines a specific type of

atom since each different type of atom(representing each element) will have a differentnumber of protons in the nucleus


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ATOMIC MASS NUMBER

the mass number has the symbol, A, and is

shown as a subscript to the element symbol

the mass number gives the mass of atom in

amu, atomic mass number, and is

approximately equal to the number of protons

plus the number of neutrons


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Law of constant composition

Reactions take place between whole numbers of

atoms at constant proportion

chemical reactions rearrange the atoms

by rearranging the atoms and their ratios ofchemical combination, the substances change

chemical reactions cannot create or destroy

matter, they can only rearrange it, thereforeall atoms in a chemical reaction product, must

have occurred within the reactants


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DNA


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Chemistry 3 Representations

Macroscopic or bulk: observations

Symbolic: written description

Microscopic/molecular: visualize atoms andmolecules

One big trick to chemistry is seeingconnections between those views

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ACHM 111,Week 2 Atoms and Molecules