Ionization Energy
For OCR and Edexcel exam boards When an atom becomes ionised it loses an electron and turns into a positive ion. Ionization energy is the energy required to remove this electron.
Definition of the first ionisation energy:
“the first ionization energy of an element is the energy required to remove one electron from one mole of atoms in the gaseous state.”
The symbol for ionization energy is ΔHi
The first ionization energy ΔHi1
An example of the first ionization energy for Calcium
Ca(g) →Ca+(g) + e- ΔHi1 = +590kJ mol-1
Definition of the second ionisation energy:
“the second ionization energy is the energy required to remove one electron from one mole of gaseous ions in the gaseous state.”
An example of the second ionization energy for Calcium
Ca+(g) →Ca2+(g) + e- ΔHi2 = +1150kJ mol-1
A general rule
The ionisation energies increase as each electron is removed. This is because the ion becomes more positively charged thus a greater force on the remaining electrons.
The three main factors influencing ionisation energies are:
1. The size of the positive nuclear charge.
This affects all the electrons. The increase of nuclear charge with atomic number will tend to increase ionisation energies.
2. The distance of electron from nucleus.
The attraction follows the inverse square law, as the distance increases the force greatly decreases. Thus electrons in the shells far from the nucleus have dramatically lower ionization energy.
3. The shielding effect by the filled inner shells.
All electrons have the same negative charge. Like charges repel thus the electrons repel each other. Electrons in filled inner shells repel electrons in outer shells and reduce the effect of the positive nuclear charge, this is called the shielding effect.
Showing posts with label Atomic Structure. Show all posts
Showing posts with label Atomic Structure. Show all posts
Thursday, 10 September 2009
The Atom and the subatomic structure for OCR and Edexcel
The Atom
GCSE and Alevel notes for OCR and Edexcel exam boards
The atomic number defines an element's position in the Periodic Table.
There are two particles contained in the nucleus these are the proton and the neutron.
GCSE and Alevel notes for OCR and Edexcel exam boards
The atomic number defines an element's position in the Periodic Table.
There are two particles contained in the nucleus these are the proton and the neutron.
Particles in the nucleus
The Proton
A proton carries a positive charge equal in magnitude and opposite in sign compared to the charge on the electron.
Thus an electronically neutral atom has the same number of protons inside the nucleus as electrons outside.
The Neutron
The mass of the atom is concentrated in the nucleus. The neutrons and protons contain nearly all of an atom's mass.
A neutron has the same mass as a proton but has no charge.
Atomic Number and Mass Number
Atomic Number (Z)
The most important difference between atoms is the number of protons in the nucleus.
This number determines the element to which the atom belongs to.
The Atomic Number Shows:
The number of protons
The number of electrons in a neutral atom
The position of the element in the periodic table
Mass Number (A)
The mass number is the total number of particles in the nucleus.
Thus the mass is the sum of the protons and the neutrons.
Atomic number (Z) = number of protons
Mas umber (A) = number of protons and neutrons
Summary Table
Particle Name | Relative Mass | Relative Charge |
Electron | 1/1846 | -1 |
Proton | 1 | +1 |
Neutron | 1 | 0 |
Isotopes
Discoved in 1913 by Frederick Soddy, isotopes are the same elements with different atomic masses. The word isotope means "equal place" referring to the fact that these atoms are positioned in the same place on the periodc table having the same atomic number but have different masses. In isotopes the number of protons must be he same but the number of neutrons varies.
For example, Hydrogen has three isotopes:
Discoved in 1913 by Frederick Soddy, isotopes are the same elements with different atomic masses. The word isotope means "equal place" referring to the fact that these atoms are positioned in the same place on the periodc table having the same atomic number but have different masses. In isotopes the number of protons must be he same but the number of neutrons varies.
For example, Hydrogen has three isotopes:
Protium | Deuterim | Tritium | |
H1 | H2 | H3 | |
Protons | 1 | 1 | 1 |
Neutrons | 0 | 1 | 2 |
Electrons
The electrons are located on the outer part of the atom. Electrons are the only components involved in chemical reactions. A model is used describes the electrons arranged in different shells. These shells have different energy levels which are occupied by the electrons. Electrons only possess energy in these fixed and stable quantised levels. When an electron would gain or lose energy it would have to move to a fixed level either higher or lower. The energy levels are commonly called shell. The shells are numbered 1,2,3,4,5 and so on. These numbers are called principle quantum numbers and have the symbol n. These numbers corresponds to the periods in the periodic table.
Shell 1 can contain a maximum of 2 electrons
Shell 2 can contain a maximum of 8 electrons
Shell 3 can contain a maximum of 18 electrons
Calculations
Number of protons = Z
Number of neutrons = A – Z
Number of electrons in a neutral atom = Z
Number of electrons in a positive ion = Z – charge on ion
Number of electrons in a negative ion = Z + charge on ion
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