Atoms, Elements & Compounds 🧪 Flashcards
Elements
A substance made of atoms that all contain the same number of protons and cannot be split into anything simpler
Compounds
A pure substance made up of 2 or more elements chemically combined. Compounds cannot be separated into their elements by physical means
Mixture
A combination of 2 or more substances (elements or compounds) that are not chemically combined. Mixtures can be separated by physical methods
Atoms
The building blocks of all matter
Atoms are made of subatomic particles
Protons
Neutrons
Electrons
One relative atomic mass unit is equal to
1/12th mass of a carbon-12 atom
Relative mass of subatomic particles
Proton= 1
Neutron= 1
Electron= 1/1840
The first shell can hold
2 electrons
The second shell can hold
8 shells
The third shell can hold
8-18 electrons
Isotopes
Isotopes are atoms of the same element that contain the same number of protons but a different number of neutrons
Isotopes display the same chemical properties because
They have the same number of electrons in their outer shells therefore the same electronic configuration and this is what determines an atoms chemistry
Isotopes have different physical properties because
The difference in mass affects physical properties such as density, boiling point and melting point
Heavy water refers to water made from
Deuterium oxide. It is 20% heavier and has a relative formula of 20. Not ideal to drink because it interferes with biochemical reactions in your cells
Relative Atomic Mass (RAM)
The average mass of isotopes of an element compared to 1/12th of the mass of the atom of C-12
(% of isotope * mass)+ (% of isotope * mass)/ 100
Ions
An electrically charged group of atoms formed by the loss or gain of electrons (this occurs to make the atom more stable)
Ionisation of metals
All metals can lose electrons to other atoms and become positively charged atoms called cations
Ionisation of non-metals
All non-metals can gain electrons from other atoms to become negatively charged ions called anions
Lattice structures
Formed by ionic compounds, consist of a regular arrangement of alternating positive and negative ions
Ionic compounds
Formed when metal atoms and non-metal ion react. The compound has no overall charge
Properties of ionic compounds
Usually solid at room temperature
High MP and BP
Good conductors of electricity in the molten state or in solution
Poor conductors in solid state
Ionic substances have high MP and BP because
of the presence of strong electrostatic forces acting on oppositely charged ions. These forces act ion all directions and a lot of energy is required to overcome them. The greater the charge on the ions, the stronger the electrostatic forces and the height the MP and BP will be.
Electrical current
For electrical current to flow there must be freely moving charged particles such as electrons or ions present so ionic compounds in molten form are good conductors of electricity in molten state or in solution as they have ions that can move and carry a charge. But solids have ions in a fixed position within the lattice and are unable to move
Covalent bonds
Formed when pairs of electrons are shared between non-metal atoms to gain a full outer shell giving them a noble gas configuration. These atoms are now called molecules
Properties of simple molecular compounds
Covalently bonded together (only a few atoms)
They have low MP and BP so they are usually liquids or gases at room temp
Poor electrical conductors
As the size of the molecules increases their MP and BP increases
Simple molecular compounds have low MP and BP because
There are only weak intermolecular forces acting between the molecules
Electrical conductivity of small molecular compounds (explanation)
There are no free ions or electrons to carry the charge so they are good insulators
Allotropes of Carbon
Diamond
Graphite
Diamond structure
Each carbon atom bonds with 4 other carbon atoms forming a tetrahedron. No intermolecular forces, very strong bonds and the substance is hard
Properties of diamond
It doesn’t conduct electricity
It has a very high MP
It is extremely hard and dense
Shiny
Uses
Jewelry
Cutting glass
The tips of drills
Structure of Graphite
Each carbon atom is bonded to 3 others forming layers of a hexagonal-shape leaving one free electron per carbon atom which exist in between layers. The layers are connected by weak vander waal’s force.
Properties of Graphite
Conducts electricity
Has a very high melting point
It is soft and slippery, less dense than diamond
Uses
Pencil lead
Lubricants
To make non-reactive electrodes for electrolysis
Structure of Silicon (IV) Oxide
Each oxygen atom is covalently bonded with 2 silicon atoms and each silicon atom is covalently bonded to 4 oxygen molecules. A tetrahedron is formed
Comparing diamond and SiO2
SiO2 has lots of very strong covalent bonds and no intermolecular forces so it has similar properties to diamond
They are both very hard and have high boiling points and are insoluble in water and don’t conduct electricity
SiO2 is cheap since it is available naturally
Uses
To make sandpaper
To line the inside of furnaces
SiO2 is found in
Sand
Metallic bonding
Metal atoms are held together strongly by metallic bonding in a giant metallic lattice. The atoms lose electrons from their outer shells and become positively charged ions. They move freely between the positive ions like a sea of electrons. Metallic bonds are strong and are a result of the attraction between the positive metal ions and the negatively charged delocalised electrons
Metals have high melting and boiling points
There are many strong metallic bonds in giant metallic structures between positive metal ions and delocalised electrons. A lot of heat energy is required to break those bonds
Metals conduct electricity because
There are free electrons available to move through the structure and carry charge. Electrons entering one end of the metal cause a delocalised electron to displace itself from the other end hence electrons can flow so electricity is conducted
Metals are malleable and ductile
Layers of positive ions can slide over one another and take up different positions. Metallic bonding is not distrusted as the outer electrons do not belong to any particular metal atom so the delocalised electrons will move with them. Metallic bonds are thus not broken and as a result metals are strong but flexible. They can be hammered and bent into different shapes or drawn into wires without breaking
