CHO3001 Flashcards
What is an atom
-building block of all chemistry
-barely visible under most powerful microscope
-all elements are made up of atoms
Atomic theory
-all atoms are made up of smaller particles : protons, neutrons, electrons
-positive protons are strongly held together in the nucleus
-neutral neutrons are found in the nucleus to prevent protons from repelling
-negative electrons are much lighter than protons and neutrons
-electrons take up most space around nucleus due to repulsion between charges
-number of protons determine the type of element
-neutral atom has equal number of protons and electrons
Mass number
Total number of protons and neutrons in the nucleus of an atom
-symbol top left
-always refers to an isotope snd never directly to an element
Isotope
An atom of the same element that has a different number of neutrons
Atomic number
-number of protons
-written on bottom left
-only refer to one element
-if number of protons change then the element changes
How to calculate number of protons, neutrons and electrons
Protons = atomic number
Neutrons = atomic number (for neutral atom)
Neutrons = mass number - atomic number
Molar mass definition
The mass of one mole of substance in grams
Where are electrons found
In energy levels
How many electrons in different energy levels
First level, up to 2
Second level, up to 8
Third level, up to 18
What is electron configuration
Arrangement of electrons in energy levels
Where are valence electrons found
Outermost energy level
Groups and valence electrons
G1, 1
G2, 2
G13, 3
G14, 4
G15, 5
G16, 6
G17, 7
G18, 8 except for helium that has only 2
What does the atomic number of an atom tell us
The amount of electrons
When are atoms more stable
When they have full valence shells (outermost energy levels)
How can atoms obtain full outer energy levels
By bonding with each other which causes them to lose energy
What are the three types of bonding
Covalent
Ionic
Metallic
What is covalent bobding
-sharing of electrons between non-metal atoms
-atoms held together by electrostatic forces between shared electrons and nuclei of the atoms
What is ionic bonding
-transfer of electrons from a metal to a non-metal atom to form cations and anions
-held together by electrostatic attractive forces
What is metallic bonding
-attraction between delocalised valence electrons and the positive core of metal atoms
Molecules
A discrete group of atoms bonded together, which retains the chemical and physical properties of that substance.
Are noble gases reactive
Group 18, noble gases are very unreactive due to their full valence shell they are stable.
Bonding theory is based on the idea that :
-atoms will share, gain or lose electrons to acquire the electron arrangement of a noble gas.
For most atoms it means acquiring 8 electrons in highest energy level.
Hydrogen, Lithium and Beryllium become stable with just two electrons in their valence shell.
Aroms can share gain or lose electrons by forming chemical bonds.
Valency
A property of atoms or groups, equal to the number of atoms of hydrogen that the atom or group could combine or displace in forming compounds.
What is the valency of an element
The combining power of the element, and can be worked out from the formula of a compound or from the periodic table.