An + ion has lost electrons, an – ion has more electrons
The atomic number is the number of
protons = the number of electron
The atomic weight/ mass number: protons +
neutrons
Notation: C12-6, 12 is the atomic weight and
6 is the atomic number
Electron configuration of the first 20 numbers:
For the first 20 numbers the following counts:
- The first shell can hold 2 electrons
- The second and third shell can hold 8
So if we look at carbon: we have an atomic mass of 6: the electronic configuration is then 2,4
If we look at calcium: we have an atomic mass of 20: the electronic configuration is then 2,8,8,2
Isotopes: atoms of an
element with the
same number of
protons but different
numbers of neutrons
(so having different
mass numbers).
- Mass
spectrometer:
,The highest number of molecule mass is the total molecule. The other peaks are isotopes
(fragmentations)
Relative atomic mass (Ar) example:
Chlorine naturally exists as two isotopes, ❑35 37
17 CL (chlorine-35) and ❑17 CL (chlorine-37). The
abundance of chlorine-35 is 75% and the abundance of chlorine-37 is 25%. In other words, in
every 100 chlorine atoms, 75 atoms have a mass number of 35, and 25 atoms have a mass
number of 37.
To calculate the relative atomic mass, Ar, of chlorine:
Ar= total mass of atoms divided by total number of atoms= ((75×35)+(25×37) ) / (75+25)
Ar= (2625+925)/100=3550/100
Ar=35.5
C-2 The periodic table
, the vertical columns
are the groups, the
horizontal rows are the
periods.
The elements are
arranged in the order
of increasing atomic
number.
Elements in the same
group have the same
chemical properties.
Metal group: reactivity
increases, non-metal
group: reactivity
decreases
Group 1: alkali metals (except for hydrogen)
Group 2: alkali earth metals
Group 16: common non-metals (covalency: 2)
Group 17: halogens (covalency: 1)
Group 18: noble gasses (covalency: 0)
Group 4-12:Transition metals
The electronic configuration of an element is related to its position on the periodic table.
The links are:
Electronic configuration feature Link to the periodic table
Number or numbers of circles Period number
Number of electrons in outermost shell Group number
Total number of electrons in all shells Atomic number
, C3. Chemical reactions, formulae and equations
In a chemical reaction new substances are formed by the rearrangement of atoms and their
electrons. No nucleus is destroyed or created.
Covalency: the amount of bonds an atom can make:
- group 18 : covalency 0
- group 17: covalency 1
- group 16: covalency 2
- group 15: covalency 3 etc…
A complete combustion: reaction products are carbon dioxide and water (use oxygen)
An incomplete combustion: reaction product is carbon monoxide.
Solid: s
Liquid: l
Gas: g
Aqueous solution: aq (when an ion is soluble Salts containing silver, lead, and mercury (I)
are insoluble.)
Chemical equations:
- ionic: always make sure the equation is neutral, so: K+ with O2- becomes 2k+ with O2-, when
a precipitation (neerslag) reaction takes place, the outcome is a solid
- half equations: an equation in which electron are taken in or out (half the equation of a
redox):
2−¿¿
O 2 +4 ⅇ−¿ →2 O ¿
- ‘normal’ equation: make sure that on each side of the arrow the substances are equal in
amount.
- Formation: A+B C, dissection: A B+C.
Equilibrium equations: ↔
- often chemical reactions can be reversible and do not go to completion. All of the reactants
do not turn fully into the products but the reaction reaches a state of equilibrium in a closed
system.
- Factors that can affect the position of the equilibrium: A ↔ B
1. temperature - if the temperature is increased, the position of equilibrium moves in the
direction of the endothermic reaction. if the temperature is reduced, the position
of equilibrium moves in the direction of the exothermic reaction.
2. concentration – When more of A is added to the equation, the reaction from A → B has
an advantage and so more of B is being made and less of A.
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