Download Unit 3. Atoms and molecules

Physics and Chemistry
Unit 3: Atoms and molecules
Unit 3. Atoms and molecules
Index
1. Elements and compounds.................................................................................................................2
1.1. Dalton's Atomic theory.............................................................................................................2
2.-The atom...........................................................................................................................................2
3.-Atomic number and mass number....................................................................................................2
4.-Isotopes, atomic mass unit and atomic mass....................................................................................3
5.-Electron configuration......................................................................................................................3
6.-Chemical Bond.................................................................................................................................4
6.1. Ionic bond.................................................................................................................................4
6.2. Covalent bond...........................................................................................................................5
6.3. Metallic bond............................................................................................................................7
Activities...............................................................................................................................................8
Practice exam........................................................................................................................................9
Periodic system..............................................................................................................................10
Page 1 of 13
Physics and Chemistry
Unit 3: Atoms and molecules
1. Elements and compounds
1.1. Dalton's Atomic theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties.
3) Compounds are formed by a combination of two or more different kinds of atoms
4) Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass and other properties.
5) Atoms of different elements combine in simple whole-number ratios to form chemical
compounds.
Activities:
1. Type the symbols:
silver, gold, iron , fluorine, oxygen, sodium, sulfur, calcium, magnesium, bromine, helium,
iodine
2. Write the elements corresponding to the following symbols:
Li, K, Rb, Cs, Be, Sr, Ba,Ni, Co, Cu, Hg, Pb, C, Si, Al, B, N, Cl, P, As, Se, Ar,
3. What...
is the most abundant element in the Universe?
is the most abundant element on Earth?
are the 4 basis chemical elements in the living organisms
4.- Write the main points of Dalton's atomic theory
5.- Give either the element or symbol that goes with each of the following:
a) sodium
f) Ag
b) sulfur
g) C
c) hydrogen
h) Si
d) lithium
i) Hg
e) helium
j) O
2.-The atom
At the end on 19th century, two particles were discovered inside the atom:
Particle
Mass
Charge
proton
1,67 10-27 Kg
+1,6 10-19C
electron
9,1 10-31 kg
-1,6 10-19 C
In the 20th century one additional particle was discovered:
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Physics and Chemistry
Unit 3: Atoms and molecules
Particle
Mass
Charge
neutron
1,67 10-27 Kg
0
So, what is an atom like?
Different atomic models were proposed in this chronological order:
Atomic model
when
structure
Thomson
1897
Solid sphere of positively charged
matter with electrons embedded
Rutherford
1911
Nuclear model with 2 distinct
areas: a positively charged
nucleus containing most of the
mass of the atom (in it were the
protons and neutrons were
suggested) and a cortex with
electrons rotating in circular orbits.
Between the nucleus and the cortex
there was a lot of space.
Bohr
1913
Similar but with definite circular
orbits. The electrons can only
travel in certain orbits (called
“stationary orbits” by Bohr: at a
certain discrete set of distances
from the nucleus with specific
energies.
Current atomic model XX century
Nuclear model with 2 distinct
areas: a positively charged
nucleus containing most of the
mass of the atom. In it, there were
protons and neutrons and a cortex
with electrons distributed in
orbitals.
Page 3 of 13
drawing
Physics and Chemistry
Unit 3: Atoms and molecules
3.-Atomic number and mass number
Atomic number, Z: The number of protons that an atom has.
Mass number, A: The number of nucleons (combined number of protons and neutrons) that an
atom has.
Name of the
element
A
Z
hydrogen
1
1
carbon
Number of
protons
Number of
electrons
6
Number of
neutrons
Symbol
8
23
11
magnesium
24
lithium
chlorine
12
3
4
35
18
oxygen
bromine
80
potassium
8
10
35
36
19
18
8
20
9
4
nitrogen
Aluminum
7
27
10
13
Be 2+
7
10
32
16
1
1
cobalt
59
arsenic
74
27
25
33
silver
S 2−
H+
33
31
15
47
46
61
iron
56
23
30
iron
56
24
30
Helium
4
Neon
20
10
10
Sodium
23
iodine
127
lead
207
P 3−
2
11
10
54
82
74
80
197
79
Au3+
19
9
cesium
mercury
200
Na
55
54
80
78
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78
F
−
Physics and Chemistry
Unit 3: Atoms and molecules
4.-Isotopes, atomic mass unit and atomic mass
Isotopes: atoms with the same atomic number but different mass number.
The kilogram is too big to measure atoms, so we use the atomic mass unit, u.
It is twelfth the mass of an atom of carbon 12 and is roughly the mass of a proton or a neutron.
The atomic mass of an element is the weighted average, according to the abundance of the
different masses of the isotopes that make up the element. The atomic mass is listed on the periodic
table.
5.-Electron configuration
It is the distribution of electrons of an atom in atomic orbitals.
Type of orbital
Number of orbitals
Electron capacity
s
1
2
p
3
6
d
5
10
f
7
14
Order of the orbital energy:
6.- Write down the name and the electron configuration of the following elements:
a) N (Z=7)
c) Cl (Z=17) e) P (Z=15)
b) Sr (Z=38) d) Mg (Z=12) f) Be (Z=4)
g) Ca (Z=20) i) Ne (Z=10) k) Fe (Z=26)
h) Br (Z=35) j) Si (Z=14)
l) I (Z=54)
Valence electrons
They are the electrons of the outer shell. The number of electrons in an atom's outermost valence
shell governs its bonding behaviour.
7.- Write down the valence electrons of the elements in the previous activity.
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Physics and Chemistry
Unit 3: Atoms and molecules
6.-Chemical Bond
Atoms are rarely isolated. Except for the noble gases, other atoms can form different groupings.
If atoms have the same atomic number, then elements are formed.
If atoms have different atomic number, then compounds are formed.
Why?
Because of their stability. Noble gases have great stability and (except helium) have 8 valence
electrons.
So, usually, all atoms want to have 8 electrons in their outer shell. They are going to do different
things (gain, lose or share electrons) to have this number (8) of electrons in the outer shell.
This is called the Octet rule.
Types of chemical bond
Based on how they get 8 electrons in the outermost shell, there are 3 types of chemical bonds:
– ionic bond
– covalent bond
– metallic bond
6.1. Ionic bond
The bond results from electrostatic attraction between ions of different charges. The transfer causes
one atom to assume a net positive charge, and the other to assume a net negative charge..
What is the chemical bond between 11Na and 17Cl like?
Element
11
Electron configuration
Valence electrons
Ion
Formula
Na
1s2 2s2 2p6 3s1
1
Na+
NaCl
Cl
1s2 2s2 2p6 3s2 3p5
7
Cl-
17
What is the chemical bond between
Element
11
11
Na and 8O like?
Electron configuration
Valence electrons
Ion
Formula
Na
1s2 2s2 2p6 3s1
1
Na+
Na2O
O
1s2 2s2 2p4
6
O2-
8
What is the chemical bond between
Element
Mg and 8O like?
12
Electron configuration
Valence electrons
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Ion
Formula
Physics and Chemistry
Unit 3: Atoms and molecules
What is the chemical bond between
Element
Cl and 20Ca like?
17
Electron configuration
Valence electrons
Ion
Formula
Ion
Formula
Ion
Formula
Ion
Formula
¿What is the chemical bond between 13Al and 17Cl ?
Element
Electron configuration
Valence electrons
What is the chemical bond between 12Mg and 7N like?
Element
Electron configuration
Valence electrons
What is the chemical bond between 9F and 3Li like?
Element
Electron configuration
Valence electrons
Properties of substances with ionic bonds
– Ionic substances require high temperatures to melt
– Solid at room temperature
– Form crystals
– Hard but brittle
– Do not conduct electricity in solid but do if dissolved in water
– Dissolve well in water
Example: table salt
6.2. Covalent bond
Atoms that share one or more pair of electrons. This type of bond is represented by Lewis diagrams.
What is the chemical bond between 9F and 9F like?
Element
Electron
Valence
Configuration
electrons
Need
Formula
F2
F
1s2 2s2 2p5
7
1
F
1s2 2s2 2p5
7
1
9
9
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Lewis diagram
Physics and Chemistry
Unit 3: Atoms and molecules
What is the chemical bond between 8O and 8O like?
Element
Electron
Valence
Need
Configuration
electrons
Formula
Lewis diagram
What is the chemical bond between 7N and 7N like?
Element
Electron
Valence
Need
Configuration
electrons
Formula
Lewis diagram
What is the chemical bond between 1H and 1H like?
Element
Electron
Valence
Need
Configuration
electrons
Formula
Lewis diagram
What is the chemical bond between 1H and 8O like?
Element
Electron
Valence
Need
Configuration
electrons
Formula
Lewis diagram
What is the chemical bond between 1H and 7N like?
Element
Electron
Valence
Need
Configuration
electrons
Formula
Lewis diagram
What is the chemical bond between 1H and 6C like?
Element
Electron
Valence
Need
Configuration
electrons
Formula
Lewis diagram
What is the chemical bond between 17Cl and 15P like?
Element
Electron
Valence
Need
Configuration
electrons
Formula
Lewis diagram
Page 8 of 13
Physics and Chemistry
Unit 3: Atoms and molecules
What is the chemical bond between 17Cl and 8O like?
Element
Electron
Valence
Need
Configuration
electrons
Formula
Lewis diagram
Properties of substances with covalent bonds
They can be:
Molecular substances
Atomic crystals
Solid, liquid or gases at room temperature
low melting point
do not conduct electricity
some dissolve well in water
Examples: water, glucose
Solid at room temperature
high melting point
do not conduct electricity
do not dissolve well in water
Examples: diamond
6.3. Metallic bond
In this type of bonding, each atom in a metal donates one or more electrons to a “sea” of electrons
that reside between many metal atoms. In this sea, each electron is free to be associated with a great
many atoms at once. The bond results because the metal atoms become somewhat positively
charged due to loss of their electrons, while the electrons remain attracted to many atoms, without
being part of any given atom.
What is the chemical bond between atoms of 11Na like?
Element
Electron
Valence
Ion
configuration
electrons
11
Na
1s2 2s2 2p6 3s1
1
Na+
Formula
Drawing
Na
What is the chemical bond between atoms of 12Mg like?
Element
Electron
Valence
Ion
configuration
electrons
Formula
Drawing
What is the chemical bond between atoms of 13Al like?
Element
Electron
Valence
Ion
configuration
electrons
Formula
Drawing
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Physics and Chemistry
Unit 3: Atoms and molecules
What is the chemical bond between atoms of 3Li like?
Element
Electron
Valence
Ion
configuration
electrons
Formula
Drawing
Properties of metallic bonds
–
–
–
–
–
They form crystals
Luster (surface light reflectivity)
Electrical and thermal conductivity
Ductility
Tensile strength
Activities
8.-
a) Write the electron configuration of: Rb (Z=37), F (Z=9) and Ca (Z=20)
b) Explain the bonding of the following combinations:
a) Rb and F
b) F and F
c) F and Ca
9.- Which of the following characteristics are related of ionic substances:
a) Form molecules
b) They conduct electricity when are dissolved
c) Do not dissolve in water
d) High melting point
10.- Name the properties of metals
11. Classify the following substances looking at the table
Substance
A
B
C
Fusion temperature
-60º C
1350º
800º C
Solubility in water
No
No
Yes
Conductivity
No
Yes
Yes
12.- Give three examples of each type of substance
13.- Circle the pairs of isotopes:
a) 12C
b)
35
17
14
C
A
14
N
35
16
B
37
17
C
14.- Explain each atomic model, writing the differences between them.
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Physics and Chemistry
Unit 3: Atoms and molecules
Practice exam
1.- Complete the following table:
Element
Z
sulphur
A
Number of
protons
Number of
electrons
32
16
18
Number of
neutrons
Atomic
symbol
56
26
potassium
19
18
Fe
20
20
10
nickel
28
gold
Ne
58
197
argon
phosphorus
3+
76
18
31
118
18
22
18
16
24
12
Mg
14
7
3−
N
2.- Give the electron configurations for the following elements, listing the number of electrons in
the outermost shell and their most likely ion:
a) Al (Z=13)
b) Br (Z=35)
c) Ca (Z=20)
d) Cd (Z=48)
e) P (Z=15)
3.- Describe the ionic bond between:
a) Potassium (Z=19) and oxygen (Z=8)
b) Nitrogen (Z=7) and magnesium (Z=12)
4.- Describe the covalent bond between:
a) Oxygen (Z=8) and hydrogen (Z=1)
b) Nitrogen (Z=7) and nitrogen
5. a) List the properties of metallic bonds. Explain a sodium crystal (Z=11).
List the properties of ionic bonds
6. Describe Thomson's, Rutherford's and Bohr's atomic models.
Page 11 of 13
Physics and chemistry
Unit 1: Matter
Periodic system
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Physics and chemistry
Unit 1: Matter
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