Download Atoms and molecules

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
Course assessment
• Course work 40%:
i.
ii.
iii.
20% Mid Term Exams
10% Laboratory work
10% Quiz
• Final Exam 60%
Total: 100%
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Chemistry and Engineering
Big stuff (objects, etc.)
Materials
Molecules
Atoms
Protons, Neutrons, Electrons
Tinier stuff (Particle Physics)
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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
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
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 same
On 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 structure
All 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
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 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.
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 compounds
Mixtures 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 sulphur
Iron – form of fillings
Sulphur- 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 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,
S8
•
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