Unit 2 - atoms, elements and compounds Flashcards
Element
A substance that can’t be broken down into anything simpler using a chemical reaction - only have 1 type of atom and each is unique
Compound
Formed when one or more atoms of different elements are joined together by chemical reactions
Mixture
Formed when two or more substances are found together but not chemically bonded to each other - can be elements or compounds - can be easily separated
Three sub-atomic particles in atoms
- Electrons
- Neutrons
- Protons
Location of sub-atomic particles
- Electrons - energy shells
- Neutrons - in the nucleus
- Protons - in the nucleus
The nucleus of an atom
- Radius of the nucleus is 10000x smaller than radius of the atom
- Most of the mass is within the nucleus because protons and neutrons have the most mass
Protons
- Number of protons = proton/atomic number
- Number of protons determines the element
- Mass of 1
- Charge of +1
Neutrons
- Mass of 1
- Charge of 0
- Atoms of the same element but different amount of neutrons are isotopes
Electrons
- Smallest sub-atomic particle
- Mass of 1/2000
- Charge of -1
- Orbit the nucleus in shells
- Number of electrons = number of protons - elements have no charge
Features of elements on the periodic table
- Nucleon/atomic mass number
- Proton/atomic number
Atomic number
- Also known as proton number
- Number of protons in an element
- Shows amount of electrons in the element too
Atomic mass Number
- Also known as nucleon number
- Number of protons + number of neutrons
Neutron calculation
Atomic mass number - Proton number
Electronic configuration
The distribution of electrons of an atom or molecule in electron shells
Amount of electrons in each shell
- First shell = Max of 2
- Second shell = Max of 8
- Third shell = Max of 8
- Fourth shell = Max of 18
- …
How to write electron configuration
- Written in the form x,x,x,
- Example - Aluminum = 2,8,3
Elements that have full shells and are uncreative
Noble gases - Group VIII
Ions
Charged atoms
What elements have to do to become stable
- Obtain a full outer shell through losing or gaining electrons
Ion charges of elements in each group
- Group 1 = 1+
- Group 2 = 2+
- Group 3 = 3+
- Group 4 = 4+-
- Group 5 = 3-
- Group 6 = 2-
- Group 7 = 1-
- Group 8 = 0
Isotopes
Atoms with the same number of protons but different numbers of neutrons
Nuclear notation
- Mass number on upper-left
- Atomic number on lower-left
- Chemical symbol on the right
- If ion, charge is on upper-right of chemical symbol
Calculating average relative atomic mass
- Average Atomic mass = Sum of [(Atomic mass x % abundance)] for each isotope ÷ 100
- Average Atomic mass = sum of [(atomic mass x relative abundance)] for each isotope ÷ sum of the relative abundance
Ionic bonding
Occurs between metal and non-metal atoms - metal donates electrons to the non-metal for both to obtain full shells
Cations
- Positive ions
- Donate electrons in bonding
- Metal atoms in ionic bonding
Diagram used for ionic bonding
Dot-and-cross diagram
Anions
- Negative ions
- Gain electrons in bonding
- Non-metal atoms in ionic bonding
Suffix for non-metals in ionic bonding
- ide e.g. fluorine –> fluoride
Forces keeping together ionic bonds
Strong electrostatic forces between positive and negative charged particles
Structure made from ionic bonding
- Giant lattice structure held together by strong electrostatic forces of attraction
Ionic bonding with incomplete electrons
- If one element can’t donate enough electrons, multiple of the element will be used e.g. lithium and oxygen
Properties of ionic compounds
- High melting and boiling points - Higher if there is higher charge since more energy is needed to break bonds and separate ions
- Conduct electricity molten or dissolved in water to make aqueous solutions, not as solid - ions can freely move molten or dissolved but not as a solid
Covalent bonds
A bond between two non-metals through the sharing of electrons
Rules of covalent bonding
- Both atoms involved must share the same number of electrons
- The number of electrons shared os qual to the number of electrons needed to fill the outer shell
- The smallest number of electrons needed are shared
Types of covalent bonds
- 1 pair of electrons bonding = single bond
- 2 pairs of electrons bonding = double bond
- …
Diagram used for covalent bonding
Dot-and-Cross diagram
Properties of covalent bonds
- Low melting point - for simple covalent molecules - large molecules need more energy and have higher melting points
- Don’t conduct electricity - don’t have charged particles that can move through the structure
Composition of diamond
- Made of only carbon
- Each carbon shares one electron with four other carbons to make a giant structure
- Known as a macromolecule
- Very hard - due to strong covalent bonds in giant structure
- Used for cutting tools
Composition of graphite
- Made of only carbon
- Each carbon shares one electron with three other carbons, fourth is delocalized
- Known as a macromolecule
- Layered hexagonal arrangement held together by weak intermolecular forces - lets layers slide
Uses of graphite
- Powder can be added to surfaces of moving parts e.g. engine parts to reduce friction
- Used as electrodes in a battery
- Electrical contacts in motors
- Electrodes in electrolysis
Composition of Silicon(IV) oxide
- Each silicon shares an electron with 4 oxygens - forms 4 covalent bonds
- Each oxygen makes two bonds with silicon atoms
Properties of Silicon(IV) oxide
- Forms transparent crystals
- Very hard - less than Diamond
- Extremely high melting and boiling points
- Do not conduct electricity - no delocalized electrons
- Do not dissolve in water
Metallic bonding
Electrons form a ‘sea’ of delocalized electrons that surround positive metal ions - held together by strong electrostatic forces of attraction - form giant metal lattice structure
Properties of metals
- High melting and boiling points - lots of energy needed to break the bonds of the lattice
- Conduct electricity - due to presence of delocalized electrons
- Malleable - layers which can move and slide past each other
- Ductile - layers can move and slide past each other
