3. Atoms, Elements And Compounds Flashcards
Define isotope
Atoms of the same element with different numbers of neutrons ( and nucleon numbers)
What is the relative mass of electron?
1/1804
One medical use of radioactive isotopes
Cancer treatment - radiation given out by the radioisotopes is used to kill cancer cells (cobalt-60)
One industrial use of isotopes
Check for leaks in oil and gas pipeline
Describe Noble Gas
They have full outer shell of electrons and so very stable
The atom cannot gain or lose electrons very easily
They are unreactive because their stability of a full outer shell
Colorless gas
Do not combine with other elements to form compound
Define element
A substance made of only one type of atom
They cannot broken down into anything simpler by chemical reacrion
What is chemical bond?
Link joining the atoms
Define compound
A substance made up of two or more different types of atoms joined together by chemical bonds
Cannot physically separate the elements in a compound
Define mixture
Contains two or more elements or compounds that are not chemically bonded together
The substances in a mixture can be separated physically
Properties of metals
Conducts electricity and heat Malleable Ductile Lustrous Sonorous
Properties of non-metals
Does not conduct heat or electricity Not malleable or ductile - brittle Dull surface Not sonorous Lower MP&BP than metal Low density Form negatively charged ions
Define alloy
Mixture of two or more elements where at least one element is a metal
Properties of alloys
Improve its properties
The other substance is often a metal
Alloys contain atoms of different size so it distorts the regular arrangement of atoms
This makes it more difficult for the layers to slide over each other => alloys are harder than the pure metal
Define ions
Charges atom
Number of protons are not equal to the number of electron
What is cations
Positively charged atom, usually metal
What is anion
Negatively charged atom, it is non-metal
What is ionic bond
The bond formed between ions of opposite charge
Properties of ions
Formed when atoms lose or gain one or more electrons
Group 1 metal gives 1 electron to the halogen if they react
Ions have the noble gas electronic structure with a complete outer shell
Giant ionic lattice structure
When do ions conduct electricity and why
When melt or dissolved because the ions are free to move
Boiling point and melting point of ions?
High BP and MP because the electrostatic force between ions are very strong
Example of alloy
Brass - 70% copper, 30% zinc)
Harder than copper, does not corrode, used in musical instruments
Define covalent bonding
When two non-metals share a pair of electrons to get full outer shells
Define valency of an atom
The number of electron lost or gain to form a complete electron shell in a covalent or ionic compound
Properties of covalent bonding
Covalent bonds within molecules are very strong
The forces between the separate molecules are weak - intermolecular force -> low melting point and boiling point
Why do ionic compounds have high melting point and boiling point
Strong forces between the ion in the giant ionic lattice
What is giant ionic lattice
Regular arrangement of alternating positive and negative ions
Compare the volatility , solubility and electrical conductivity of ionic compounds and covalent compounds
Ionic - low volatility, usually soluble in water, conduct when molten or dissolved in water
Covalent - high volatility, insoluble in water, don’t conduct
What is giant covalent structure
Network of covalent bonds through out the whole structure
Rigid 3D network of strong covalent bonds throughout the crystal so lots of energy to break the bond. They have high mp and bp
Define allostropes
Different forms of the same element
Describe the structure of diamond
A carbon atom forms 4 covalent bonds with other C atoms
Carbon atoms link together to form a giant lattice
High mp and bp
Very hard and cant be scratched easily -> use for cutting and drilling metal and glass
Does not conduct
Forms colorless glittering crystals -> use for jewellery
Properties of graphite
Black and shiny solid
Carbon atoms are arranged in layers
Each C atom is joined to 3 other C atoms
Arranged in hexagon
Strong covalent bond within the layers=> a lot of energy is needed to break the bond -> high mp and bp
Bonding between layers is weak -> layers can slide over each other -> slippery feel and easily scratched
Weak bonding -> layers can flame off easily -> use as lubricant and in pencil
Conducts electricity
Why does graphite conduct electricity?
Each C atom is bonded to 3 other C atom
C has 4 valency electrons
=> there are delocalized electrons move around along the layers
=> they drift along the layer when voltage is applied
Properties of silicon(IV) dioxide
Makes up most of sand
Each silicon atom is bonded to 4 O atoms
Each Oxygen atom is bonded to 2 silicon atoms
Forms very hard colorless crystals -> high MP and BP
Does not conduct electricity bc it has no delocalized electrons
What is metallic bonding?
Lattice of positive ions in a sea of electrons
Why metal have high BP and MP?
It takes a lot of energy to weaken the strong force of attraction between the metal ions and delocalized electrons in the lattice
Why metals are good conductor of heat and electricity
Delocalised electrons move through the metal lattice and carry energy through the metallic structure quickly
Conduction of heat is due to vibrations of the atoms passing on the energy form one atom to the next
The metallic structure allows the atoms to vibrate more freely
Why are metals malleable and ductile?
Positive ions arranged regularly in layers so when force is applied, layers can slide over each other and new bond can easily form - this is because the attractive forces between the metal ions and the electrons act in any direction
What is Ar?
Average mass of the atoms of an element, relative to thr mass of an atom of carbon 12
What is Mr?
The sum of the relative atomic masses, call the relative molecular mass
