These exercices have been translated from
Websciences
1
Find the particles of the following atoms:
1.
;
;
.
2. Carbon 14, Uranium 238.
Correction
You must look at your perodic table to collect the data. The number that you'll find in top of the element is the mass numberA.1. The chlorine atomClhas atomic number Z=17 and mass number A=35. The nucleus of chlorine contains therefore17 protons (Z) and18 neutrons (A-Z). Around the nucleus there are 17electrons (the atom is electrically neutral and so it has the same number of electrons and protons).
The sodium atomNa has atomic number Z=11 and mass number A=23. The nucleus of sodium contains therefore 11 protons (Z) and12 neutrons(A-Z). Around the nucleus there are11electrons.
ThecobaltatomCo has atomic number Z=27 and mass number A=59. The nucleus of cobalt contains therefore 27 protons (Z) and 32 neutrons(A-Z). Around the nucleus there are27electrons.
2. This carbon atomC has atomic number Z=6 and mass number A=14. The nucleus of this carbone atom contains therefore 6 protons (Z) and 8 neutrons(A-Z). Around the nucleus there are6electrons.
The uranium atomU has atomic number Z=92 and mass number A=238. The nucleus of uranium contains therefore 92 protons (Z) and 146 neutrons(A-Z). Around the nucleus there are92electrons.
2
Find the particles of the following ions:
1.
;
.
2.
;
.
Correction
1.The bromide ion Br- has atomic number Z=35 and mass number A=79.The nucleus of this ion contains therefore 35 protons(Z) and 44 neutrons (A-Z). Around the nucleus there are 36 electrons ( attention , the atom has 35 electrons,but the bromide ion Br- has a supplementary negative charge).
The sulfide ion S2- has atomic number Z=16 and mass number A=32. The nucleus of sulfide ion contains therefore 16 protons(Z) and 16 neutrons (A-Z). Around the nucleus there are 18 electrons (2 electrons more than the corresponding atom which has 16).
2. The cesium ion Cs+ has atomic number Z=55 and mass number A=133. The nucleus of cesium ion contains therefore 55 protons(Z) and 78 neutrons (A-Z). Around the nucleus there are 54 electrons ( Attention, the atom has 55 electrons, but the cesium ion Cs+ has a supplementary positive charge).
The zinc ionZn2+ has atomic number Z=30 and mass number A=64. The nucleus of zinc ion contains therefore 30 protons(Z) and 34 neutrons (A-Z). Around the nucleus there are28 electrons (2 electrons less than the corresponding atom which has 30).
3
The nucleus of an atom contains 17 protons and 18 neutrons.
1. What is its number of electrons?
2. What is its mass number?
3. What is its atomic number?
4. Identify the element!
Correction
1.An atom is electrically neutral. It has as many electrons as protons. This atom has 17 protons, so it must have 17 electrons. 2. This atom has 17 protons and 18 neutrons. Its mass number is therefore A=35(17 + 18). 3. The atomic number is Z=17(17protons). 4. Z=17, it is a chlorine atom with symbol Cl .
4
Two atoms have 14 neutrons. The first has 13 protons and 13 electrons and the second 14 protons and 14 electrons.
Are those atoms isotopes of the same chemical element?
Why?
Correction 4
Isotopes have the same number of protons (they belong to the same chemical element), but different numbers of neutrons . Therefore they have the same atomic number Z, but not the same mass number A. These atoms are not isotopes as they don't have the same atomic number.
5
Determine the structure of the nucleus and the number of electrons of.
1. Atom
2. Ion
formed from the atom
3. Ion
formed from the atom
Correction
1.
The lithium atom Li has atomic number Z=3 and mass number A=7.
The nucleus of lithium contains therefore 3 protons (Z) and 4 neutrons (A-Z).
Around the nucleus we will find 3 electrons (Being electrically neutral, the atom has as many protons as electrons).
2.
The aluminium ion Al3+ has atomic number Z=13 and mass number A=27.
The nucleus of aluminiumion contains therefore 13 protons(Z) and 14 neutrons (A-Z).
Around the nucleus we will find 10 electrons
( Attention, the corresponding atom has 13 electrons, but the Al3+ ion has 3 elementary positive charges more, and therefore 3 electrons less).
3.
Sulfide ion S2- has atomic number Z=16 and mass number A=32.
The nucleus of sulfide ion contains therefore 16 protons(Z) and 16 neutrons (A-Z).
Around the nucleus we will find 18 electrons (2 electrons more than the corresponding atom which has 16).
6
We will admit that the mass of an aluminum atom
$^{27}Al$
equals the mass of its particles.
1.
Calculate the mass of the aluminium nucleus !
2.
Calculate the mass of its electrons ! Compare !
3.
Calculate the mass of one aluminium atom !
4.
The mass density of aluminium is ρ=2.7·103kg.m-3.
Calculate the mass of an alumium cube with a side length of 2cm?
How many atoms are there in this cube?
Given:Mass of one proton:
mp=1.673·10-27kg.
Mass of one neutron: mn=1.675·10-27kg.
Mass of one electron: me =9.109·10-31 kg.
Correction
1.
The aluminium atom has atomic number Z=13 and mass number A=27.
The nucleus of alumium contains therefore 13 protons(Z) and 14 neutrons (A-Z).
The mass of the nucleus is therefore:
number of protons ·mass of one proton + number of neutrons · mass of one neutron .i.e.
m=Z.mp+(A-Z)·mn.
mnucleus=
13·1.673.·10-27 + 14·1.675·10-27mnucleus=
4.520·10-26kg.
2.
Around the nucleus we have 13 electrons.
The mass of the electron cloud is therefore:
melectrons =
13x9.109·10-31melectrons=1.184·10-29kg.Attention:
mnucleus/melectrons =
4.520·10-26/1.184·10-29=
3817.56.
The mass of the electron cloud is negligible compared with the mass of the nucleus.
3.
The total mass of the alumium atom is:
mAl =
mnucleus+melectrons
mAl=4.520·10-26+1.184·10-29
mAl=4.521·10-26kg=
more or less mnucleus.
4.
The volume of the cube is V=(2.10-2)3.
V=8.00·10-6m3.
The mass of this cube is
m=ρ.V m=2.7·103x8.00·10-6
m=22·10-3kg (22g).
The cube contains
n=m/mAl atoms.
i.e.: n = 22·10-3/ 4.521·10-26n = 4.77·1023 atoms
(enormous number).
;
;
.
2. Carbon 14, Uranium 238.
;
.
2.
;
.
2. Ion
formed from the atom
3. Ion
formed from the atom
