General information

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

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Chemistry and Engineering

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Advice

• If you are worried about chemistry, don’t 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 guessing

what might be on exams

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Atoms and molecules

ACHM 111

Particles

• Atoms• molecules

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 smallest

particles that can exist and represent elements identity. Atoms cannot be

created or destroyed

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

ATOMIC STRUCTURE

ATOMIC STRUCTURE

PropertiesParticle 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

Atoms

• Sub-atomic particles• Electrons• Protons• neutrons

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 their

properties are summarized in the following table • neutrons – neutrons have no charge and their properties are

summarized in the following table

ELECTRONS

• Small negatively charged particle• Orbit, circle, around the nucleus• Have no mass.• Atoms are neutral.• Number of electrons = number of protons

PROTONS:

• small, positively charged particles • reside in the nucleus • along with the neutron, make up most of the

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

NEUTRONS:

• small particles with no charge • reside in the nucleus • along with the proton, make up most of the

mass of the atom • a differing number of neutrons is what defines

an "isotope" of an atom

ATOMS--Dalton's Atomic Theory

• All matter (including elements) is composed 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

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

What's a molecule?

Definition:The smallest particles of an element or compound that can exist and retain the chemical properties of that element or

compound

Molecules

•Molecular formula gives composition: number of atoms of each element present•Molecular mass= sum of masses of atoms

EXAMPLES OF MOLECULES

Examples of molecules

Atomicity The 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 a few well-known cases of higher atomicity, such are ozone O3 and white phosphorus P4. in this sense the molecule is also the smallest particle of a compound that can exist in the free state.Definition: the atomicity of a substance whether an element or a compound is the number of atoms in one molecule.

Representing molecules

• Names: ethanol, ethyl alcohol

•Formulas: C2H8O, C2H5OH, CH3CH2OH

•Structural drawings

•Models

Formula

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.

Atomic and molecular structureAll matter living or dead consists of materials. In nature their are 116 fundamental materials these are called elements.Definition: an element is a substance that cannot be split 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 smaller than atoms known as electrons, protons and neutrons

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 changerMolecules: atoms of an element may not be able to exist singly: the atomicity of an element is the number if the atoms in on moleculeDefinition: the molecule is the smallest particle of an element which can exist in the free state under ordinary conditions.

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

Mixtures

A pure substance is one in which all the molecule alike. Element and compounds are the only pure substances that 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 and difficulty 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

Mixtures and compoundsMixtures and compounds both contain more than one element and so should be separable into their component elements. This process may be easy or difficult but it is not the only criterion for deciding whether a given material is a mixture or a compound.Example: consider two elements iron and sulphurIron – form of fillingsSulphur- form of yellow powderMix them together without heat mixtureHeat mixture in a test tubeThis process of water of crystallization in a substance e.g. copper sulphate -5- water does not make it a mixture because the composition is fixed.

Pure substances

Element, Atom, Compound, Molecule

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

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

• A compound is a substance which contains two or more kinds of atoms: carbon dioxide (CO2), calcium oxide (CaO), sodium hydroxide (NaOH).

• A molecule is the smallest particle of a substance which exhibits the physical 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

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 very dense, 99.95% (or more) of the mass of the atom is in the nucleus which has a diameter of approximately 10 -15 m-- a matchbox of nucleus material would weigh 2½ billion tons! The density is approximately 1013 - 1014 g/cm3.

– Rutherford discovered this through his famous experiment with gold foil in which he shot alpha particles (fairly massive particles with a positive charge) through thin gold foil and found that many particles were strongly deflected and some bounced back at him! This could only happen if the gold foil atoms contained massive centers that had a positive charge, as exhibited in the figure below.

Atomic structure

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

ATOMIC NUMBER:

• • the atomic number has the symbol, Z, and is

shown as a superscript to the element symbol • the atomic number gives the number of protons

in the nucleus (and the number of electrons if the species 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 different number of protons in the nucleus

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

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 of chemical

combination, the substances change

• chemical reactions cannot create or destroy matter, they can only rearrange it, therefore all atoms in a chemical reaction product, must have occurred within the reactants

DNA

Chemistry 3 “Representations”•Macroscopic or bulk: observations

•Symbolic: written description

•Microscopic/molecular: visualize atoms and molecules

•One big trick to chemistry is seeing connections between those views