Date post: | 27-Dec-2015 |
Category: |
Documents |
Upload: | hortense-harrison |
View: | 213 times |
Download: | 0 times |
ATOMIC STRUCTURETHE HALF OF KNOWLEDGE IS KNOWING WHERE TO FIND KNOWLEDGE. UNKNOWN
Ch2. 1. J.C. Rowe
Windsor University School of Medicine
CONCEPT MAPElements,
compounds & mixtures
Separation methods Solutions
Atoms have structure
Atomic nucleus
Electronic structure
Size of atoms
Atoms & ions
Symbols for atoms & ions
Elements, Mixtures and Compounds
Elements: Are materials that could not be separated into simpler things
either physically or chemically Elements contain only one type of atom Iron is an example of an element
Mixture: Composition of two or more substances that can be separated
physically Example of a chemical mixture is the combination of Sand and
Salt
Compound: Combination of two or more elements The units of a compound have different properties
Compounds have fixed compositionsExample – combination of Iron and Sulphur.
Mixtures
• What is a mixture?
• How can it be separated?
• A mixture is a physical blend of two or more substances.
• Their composition varies (Air).
• There are two types of mixtures: homogenous and heterogenous
Homogenous or Heterogenous?
1. Air
2. Salt water
3. Tea
4. Brass
5. Vinegar
6. Hydrogen peroxide
7. Steel
1. Salad dressing
2. Apple
3. Sand
4. Paint
5. Granite
6. Laundry detergent
7. Cereal
Heterogenous Mixtures Is the type of mixture that is not uniform in
composition.
If one portion of the above mixture were sampled, it’s composition would vary.
Homogenous Mixtures Is a type of mixture that has a completely
uniform composition throughout. It’s components are evenly distributed
throughout the sample.
Solutions
• Is the special name that scientists give to homogenous mixtures.
• Solutions may be of gases, liquids or solids.
• An example:
solution of sugar solid in liquid water.
What is a Solution ?Ques:
• A Mixture of 2 or more soluble substances dissolved in a solvent
• Can you name any solutions ?
What is a solution ?
Solutions are a special kind of mixture.
Solution = solvent (major) + solute (minor).
A solvent may be a solid, a liquid or a gas.
When the solvent is a liquid the solution is said to be aqueous (water) or non-aqueous (other than water).
Solution can be homogeneous or
heterogeneous.
Solutions
Some common types of solutionsSome common types of solutions
System Examples System Examples
Gas-gasGas-gas COCO2 2 and O in N (air) and O in N (air)
Liquid-gasLiquid-gas Water vapor in airWater vapor in air
Gas-liquidGas-liquid COCO22 in in HH22O (Soda water)O (Soda water)
Liquid-liquidLiquid-liquid Acetic acid in HAcetic acid in H22O (vinegar)O (vinegar)
Solid-liquidSolid-liquid NaCl in NaCl in HH22O (brine)O (brine)
Solid-solidSolid-solid Cu in Ag (Sterling silver)Cu in Ag (Sterling silver)
Separating Mixtures
If you were given a mixture of iron nails, salt and water…
How would you separate this mixture completely?
Based on which physical properties would you base your method on?
Separating Mixtures
How would you separate the components in tap water?
Distillation
A liquid is boiled to produce vapor that is then condensed again to a liquid
Separating Mixtures
Conditions for solubility
Temperature Solids usually are more soluble in liquids
as the temperature increases; Gases are less soluble in warm water than
cold water; Gases dissolve more in liquids at higher
pressure. Ionic materials dissolve in water Covalent materials dissolve in
covalent liquids
Separating mixtures
Filtration
Evaporation
Distillation/fractional distillation
Gravity separation
chromatography
The nuclear atom
Rutherford showed in 1911 that atoms:
Have a very tiny nucleus at the center Have all their positive charge in the
nucleus Have almost all their mass in the nucleus Have only negative electrical charges
making up the rest of their volume
Model of an Atom
The Rutherford Experiment
Properties of the 3 sub-atomic particles
Name of particle
symbol Relative mass
charge location
Electron e 0 -1 Always outside the nucleus
Neutron n 1 0 Always in the nucleus
Proton p 1 +1 Always in the nucleus
Protons/Mass number/Isotope The atomic number of an element is the
number of protons in an atom of that element.
The mass number of an element is the sum of the number of protons & the number of neutrons in one atom of that element.
Isotopes of an element are atoms of that element containing the same number of protons but different numbers of neutrons.
Standard Atomic Notation
Radioactivity
If there are the “wrong” number of neutrons in a nucleus, the atom changes to get the number right. The atom fires out one or more fragments from its nucleus. This type of change is called radioactivity.
The changing radioactive atoms are said to
decay.
Electron shells
The electrons are not moving at random in the space around the nucleus.
They are arranged in layers, one outside the other. These layers of electrons are called electron shells.
A shell can only hold up to a maximum number of electrons. (2n^2)
1rst shell (2electrons); 2nd shell (8electrons) 3rd shell (18electrons); 4th shell (32
electrons)
Atoms & ions
Atoms are electrically neutral. Removing an electron from an atom
leaves the atom with a net positive charge.
Adding an extra electron to an atom gives it a net negative charge.
Charged atoms or groups of atoms are called ions.
Atoms vs. ions
Symbols for some common atoms & ions
Atom or ion
symbol Proton #
# of electrons
Net charge
Chlorine atom
Cl 17 17 0
Chloride ion Cl- 17 18 -1
Iron atom Fe 26 26 0
Iron ion Fe2+ 26 24 +2
Nitrate ion NO3- * * -1
Oxide ion O2- 8 10 -2
Sodium atom
Na 11 11 0
Sodium ion Na+ 11 10 +1
Sulphate ion SO42- * * -2
An ion is an atom, or group of atoms, that has a net positive or negative charge.
cation – ion with a positive chargeIf a neutral atom loses one or more electronsit becomes a cation.
anion – ion with a negative chargeIf a neutral atom gains one or more electronsit becomes an anion.
Na 11 protons11 electrons
Na+ 11 protons10 electrons
Cl 17 protons17 electrons
Cl-17 protons18 electrons
2.5
HISTORY OF THE ATOMHISTORY OF THE ATOM
460 BC Democritus develops the idea of atoms
he pounded up materials in his pestle and
mortar until he had reduced them to
smaller and smaller particles which he
called
ATOMAATOMA
(greek for indivisible)
Dalton’s Atomic Theory (1808)1. Elements are composed of extremely small
particles called atoms. All atoms of a given element are identical. The atoms of one element are different from the atoms of all other elements.
2. Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same.
3. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.
2.1
8 X2Y16 X 8 Y+
2.1
2
2.1
HISTORY OF THE ATOMHISTORY OF THE ATOM
1913 Niels Bohr
studied under Rutherford at the Victoria
University in Manchester.
Bohr refined Rutherford's idea by
adding that the electrons were in
orbits. Rather like planets orbiting the
sun. With each orbit only able to
contain a set number of electrons.
Bohr’s Atom
electrons in orbits
nucleus
HELIUM ATOM
+N
N
+-
-
proton
electron
neutron
Shell
What do these particles consist of?
ATOMIC STRUCTUREATOMIC STRUCTURE
Particle
proton
neutron
electron
Charge
+ ve charge
-ve charge
No charge
1
1
nil
Mass
ATOMIC STRUCTUREATOMIC STRUCTURE
HeHethe number of protons and neutrons in an atom
44Atomic mass number
the number of protons in an atom
22Atomic number
number of electrons = number of protons
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
Rutherford’s Model of the Atom
2.2
Chadwick’s Experiment (1932)
H atoms - 1 p; He atoms - 2 p
mass He/mass H should = 2
measured mass He/mass H = 4
+ 9Be 1n + 12C + energy
neutron (n) is neutral (charge = 0)
n mass ~ p mass = 1.67 x 10-24 g
2.2
Subatomic Particles
Particle Mass
(g) Charge
(Coulombs) Charge (units)
Electron (e-) 9.1 x 10-28 -1.6 x 10-19 -1
Proton (p) 1.67 x 10-24 +1.6 x 10-19 +1
Neutron (n) 1.67 x 10-24 0 0
mass p = mass n = 1840 x mass e-
2.2
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different numbers of neutrons in the nucleus
XAZ
H11 H (D)2
1 H (T)31
U23592 U238
92
Mass Number
Atomic NumberElement Symbol
2.3
2.3
Period
Group
Alkali M
etal
Noble G
as
Halogen
Alkali E
arth Metal
2.4
ATOMIC STRUCTUREATOMIC STRUCTURE
Electrons are arranged in Energy Levels
or Shells around the nucleus of an atom.
• first shell a maximum of 2 electrons
• second shell a maximum of 8
electrons
• third shell a maximum of 8
electrons
ATOMIC STRUCTUREATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1. Electronic Configuration
2. Dot & Cross Diagrams
ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
With electronic configuration elements are
represented numerically by the number of
electrons in their shells and number of shells. For
example;
N
Nitrogen
14
2 in 1st shell
5 in 2nd shell
configuration = 2 , 5
2 + 5 = 7
7
ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements;
Ca O
Cl Si
Na20
40
11
23
8
17
16
35
14
28B
11
5
a) b) c)
d) e) f)
2,8,8,2 2,8,1
2,8,7 2,8,4 2,3
2,6
DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS
With Dot & Cross diagrams elements and
compounds are represented by Dots or Crosses to
show electrons, and circles to show the shells. For
example;
Nitrogen N XX X
X
XX
X
N7
14
DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS
Draw the Dot & Cross diagrams for the following elements;
O Cl8 17
16 35a) b)
O
X
XX
X
X
X
X
X
Cl
X
X
X
X X
X
XX
X
X
X
X
X
XX
X
X
X
SUMMARYSUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus.
2. The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
3. The number of Protons = Number of Electrons.
4. Electrons orbit the nucleus in shells.
5. Each shell can only carry a set number of electrons.
2.6
A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance.
An empirical formula shows the simplest whole-number ratio of the atoms in a substance
H2OH2O
molecular empirical
C6H12O6 CH2O
O3 O
N2H4 NH2
2.6
ionic compounds consist of a cation and an anion
e.g. NaCl is really composed of Na+ & Cl _
• the formula is always the same as the empirical formula
• the sum of the charges on the cation and anion in each formula unit must equal zero… Is this always true?
The ionic compound NaCl
2.6
The term molecule is not normally used to apply to ionic substances.. Can you guess why?
The?
Formula of Ionic Compounds
Al2O3
2.6
2 x +3 = +6 3 x -2 = -6
Al3+ O2-
CaBr2
1 x +2 = +2 2 x -1 = -2
Ca2+ Br-
Na2CO3
1 x +2 = +2 1 x -2 = -2
Na+ CO32-
Some Polyatomic Ions
NH4+ ammonium SO4
2- sulfate
CO32- carbonate SO3
2- sulfite
HCO3- bicarbonate NO3
- nitrate
ClO3- chlorate NO2
- nitrite
Cr2O72-
dichromate SCN- thiocyanate
CrO42- chromate OH- hydroxide
2.7
Chemical Nomenclature• Ionic Compounds
– often a metal + nonmetal– anion (nonmetal), add “ide” to element name
BaCl2 barium chloride
K2O potassium oxide
Mg(OH)2magnesium hydroxide
KNO3 potassium nitrate
2.7
• Transition metal ionic compounds– indicate charge on metal with Roman numerals
FeCl2 2 Cl- -2 so Fe is +2 iron(II) chloride
FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride
Cr2S3 3 S-2 -6 so Cr is +3 (6/2) chromium(III) sulfide
2.7
• Molecular compounds1. nonmetals or nonmetals + metalloids
2. common names
• H2O, NH3, CH4, C60
3. element further left in periodic table is 1st
4. element closest to bottom of group is 1st
5. if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom
6. last element ends in “ide”… this only applies for members of Group 5, 6, & 7
2.7
HI hydrogen iodide
NF3 nitrogen trifluoride
SO2 sulfur dioxide
N2Cl4 dinitrogen tetrachloride
NO2 nitrogen dioxide
N2O dinitrogen monoxide
Molecular Compounds
2.7
TOXIC!
Laughing Gas
A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds
H2 H2O NH3 CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
2.5
Quality is never an accident. It is always the result of high intention, sincere effort and skillful execution. It represents the wise choice of many alternatives.
unknown