Define an atom.
An atom is the smallest particle that can still have the chemical characteristics of an element.
What does the term nucleons refer to?
protons and neutrons are collectively nucleons.
What the sub atomic particles and their relative charges?
proton: 1+ , mass = 1
neutron: 0, mass = 1
electron: 1-, mass = ¹⁄₁₈₄₀
Describe electrons.
Electrons orbit around the electron shells. The number of electron shells of an atom are represented by their Periods in the Periodic Table. E.g.: atoms of elements in period 2 have two electron shells. Electron shells have different energy levels, with the one closest to the nucleus as the lowest energy level. The further the electron shell is from the nucleus, the higher its energy level and the less stable the electrons will be.
higher energy = less stable
e.g. Ar has higher energy than Ne and He.
Define proton and nucleon number.
The proton number (Z) of an atom is the number of protons in its nucleus. This number is also called the atomic number.
The nucleon number (A) is the total number of protons and neutrons in the nucleus. This number is also known as the mass number.
What nuclide notation?
Mass number above the element and proton number below.
E.g. 9 19
F in periodic table vs. F in nuclide.
19 9
Define ion.
An ion is the particle formed when an atom or group of atoms gains or loses electron(s), but the number of protons and neutrons remains the same.
ions are formed when atoms lose or gain electrons resulting in a charged particle as the number of protons and electrons are not equal.
They can be represented through the use of charge numbers, which indicate how many electrons have been gained or lost.
Define element.
Elements are the basic building blocks of living and non-living matter. They are pure substances that cannot be broken down into two or more simpler substances by chemical methods, and they only consist of one type of atom.
What are isotopes?
Isotopes are atoms of the same element that have the same number of protons but different number of neutrons.
Isotopes have similar chemical properties, as their number of valence electrons are the same. The isotopes will undergo the same kind of chemical reactions. Isotopes have different physical properties, as their masses are different due to different number of neutrons. Such physical properties may include density, melting point and boiling point.
What are the uses of isotopes?
Some isotopes can emit high-energy radiation that can damage living cells. These isotopes are radioactive substances called radioisotopes. However, when handled safely and carefully, these isotopes can be useful.
e.g.
carbon-14 for estimating the age of things that contain carbon
iodine-131 for the treatment of thyroid disorder.
How do we find the relative atomic mass of an element using the abundance of its isotopes?
relative atomic mass = (relative abundance of isotope 1 x atomic mass of isotope 1) + (relative abundance of isotope 2 x atomic mass of isotope 2) and so on….
e.g.
Cl-35 is 75%, while Cl-37 is 25%. Calculate the relative atomic mass of Cl atom.
75% x 35 + 25% x 37 = 35.5
How to find the abundance of an isotope using only the relative atomic mass of the atom and atomic masses of the isotopes?
Let x be the % of (isotope),
(relative atomic mass) = (ˣ⁄₁₀₀ x atomic mass of isotope 1) + (¹⁰⁰⁻ˣ⁄₁₀₀ x atomic mass of isotope 2)
then solve for x.
e.g. Cl-35, Cl-37 are isotopes. The relative atomic mass of Cl is 35.5. Find the abundance of Cl-35.
let x be % of Cl-35,
35.5 = (ˣ⁄₁₀₀ x 35) + (¹⁰⁰⁻ˣ⁄₁₀₀ x 37)
.
.
.
x = 75
therefore, the abundance of Cl-35 is 75%.
How are electrons arranged in the atom?
In atoms, electrons are arranged around the nucleus of an atom in electron shells. They are constantly moving around the nucleus of the atom. Electrons have different energies and can be grouped based on their energy levels in zones known as electron shells. Electrons in the innermost shell have the lowest energy, and those in the outermost shell (furthest away from the nucleus) have the highest energy. Electrons will occupy the lowest energy levels (inner shells) first. The first electron shell holds a maximum of 2 electrons. From the second electron shell onwards, the outermost electron shell of an atom holds a maximum of 8 electrons.
What are is a valence shell and valence electrons?
Theo outermost shell is called valence shell. The electrons in the valence shell are called valence electrons.
How do we find valence electrons using periodic table?
Elements in the same group will have the same number of valence electrons.
Elements in grps 1 and 2 will hv 1 and 2 valence electrons respectively. Groups 13 - 18 will have 3 to 8 valence electrons respectively (with the exception of helium).
Describe the trends across the period (left to right) and down the group (top to bottom) in the periodic table.
Period (left to right):
- Atomic number increases, number of electrons increases.
-Elements change from metallic to non-metallic.
Group (top to bottom):
- Increase in the number of electrons shells, leading to larger radius for the elements and larger elements (e.g. K is larger than Na).
- Weaker attractive force between nucleus of atom and valence electrons.
- Elements w the same number of valence electrons are in the same group. The chemical properties of an element is largely dependent on the number of valence electrons it has.
- Electrons in the same group have similar chemical properties, as the number of valence electrons is the same. E.g. group 1 metals such as lithium, sodium and potassium react with water to form alkali and hydrogen gas.
