Key Concepts Flashcards
What are the three ideas in John Daltons theory about the atom?
Atom cannot be created, divided or destroyed, atoms of the same element are exactly the same and atoms of different enemy’s are different and atoms join with other atoms to make new substances
What discovery caused the original Dalton model of an atom to change?
The discovery of subatomic particles
How did JJ Thomson discover the electron?
Thomson experiment with a cathode ray tube, the beam moved towards the positively charged plate so he knew that the particles must have a negative charge
What was the atomic model proposed by JJ Thomson?
Plum pudding model, negatively charged electrons scattered through a positively charged material
What did Ernest Rutherford discover from his gold foil experiment?
He shot a beam of positively charged particles at sheet of foil, most of the particles passed straight through suggesting that atoms were mostly empty space and a few particles were deflected and a few bounced directly back showing that there must be a tiny, dense and positively-charged nucleus
What is Rutherfords new model of the atom like?
Mass is concentrated in the central nucleus, mostly empty space and electrons travel in random paths around the nucleus
What is the structure of an atom?
Small central nucleus made up of protons and neutrons and electrons orbit the nucleus in shells
What is the radius of the nucleus?
The radius of the nucleus is 1 x 10-14 m (thus is 1/100000 of the atomic radius)
What are the relative masses of the subatomic particles?
Proton: 1, neutron: 1 and electron: 1/1836
What are the relative charges of the subatomic particles?
Proton: +1, neutron: 0 and electron: -1
Why do atoms contain equal numbers of protons and electrons?
Atoms are stable with no overall charge, protons are positively charged and electrons are negatively charged,for the charges to valence, the number of protons and electrons must be equsl
Where is the mass of an atom concentrated?
In the nucleus
What does the atomic number of an atom represent?
The number of protons
What does the mass number of an atom mean?
Number of protons and neutrons found in the nucleus of the atom
What is an isotope?
Atoms with the same number of protons but a different number of neutrons
Why is the relative atomic mass not always a whole number?
Different isotopes of the same have different mass number, the relative atomic mass is an average of the masses of all these isotopes
How did Mendeleev arrange the events in his periodic table?
Elements arranged with increasing atomic masses, elements with similar properties put into groups, switched the positions of some elects and left gaps for undiscovered elements
How was Mendeleev able to predict the properties of new elements?
Mendeleev left gaps in his periodic table, he used the properties of elements next to these gaps to predict the properties of undiscovered elements
Why was Mendeleev table lacked some amount of accuracy in the war he’d ordered his elements?
Isotopes were poorly understood at the time and protons and neutrons hasn’t been discovered
How are elements arranged in the modern periodic table?
In order of increasing atomic number
What do elements in the same group have similar?
Chemical properties
Why do elements in the same column have similar chemical properties?
Same number of out shell electrons and number of outer shell electrons determines how an atom reacts
What does the period number tell you about all the elements in that period?
Same number of electrons shells
What does the group number tell you about all the elements in that period?
same number of outer electrons
On which side of the periodic table are the metals positioned?
Left hand side
What determines whether an element is a metal or non-metal?
Atomic structures of the elements
When are atoms most stable?
When they have full electron shells
How is the electron configuration of an element related to its position in the periodic table?
The number of rings is the period and number of electrons in the outer ring is the group
What is an ionic bond?
A bond between a metal and non-metal involving the transfer of electrons
What happens to the metal and non-metal when an ionic bond forms?
The metal atom loses electrons to become a positively charged ions (cation) and non-metal gain’s electrons to become a negatively charged ion (anion)
What is an ion?
An ion is an atom or group of atoms with a positive or negative charge
Has an ion, which is positively charge, lost or gained electrons?
It had lost electrons, there are fewer negatively charged electrons to cancel out the charge of the positive protons, this means the overall charge becomes positive
Why do elects in group 1, 2, 6 and 7 readily form ions?
So they become more stable and achieve the electron structure of the noble gases (group 8)
Why type of ions ions do elements in group 1 and 2 form?
Cations (positive)
Why type of ions ions do elements in group 6 and 7 form?
Negative
What does it mean if an ionic compound ends in -ide?
The compound contains 2 elements
What does it mean if an ionic compound ends in -ate ?
The compound contains at leaf three element, one of which which is oxygen
What is the structure of an ionic compound like?
Lattice structure, regular arrangement of ions, ions held together by strong electrostatic forces between ions with opposite charges
What is a covalent bond?
A bond formed when an electron pair shared between two atoms
What forms as a result of covalent bonding?
A molecule
Are covalent bonds weak?
No, they are strong
Which is smaller, an atom or a molecule?
An atom, simple molecules consist of atoms joined by strong covalent bonds within the molecule
Why do ionic compounds have high melting points?
Strong electrostatic attraction between the positive and negative ions requires a lot of energy to overcome
When and why do ionic compounds electricity?
When molten or aqueous because the ions are charged and free to move, when solid the ions are fixed in an ionic lattice so can’t move
Why do simple molecular compounds have low melting and boiling points?
They have weak intermolecular forces which only require a little energy to overcome
Why do simple molecules compound don’t conduct electricity?
There are no charge particles
Why do giant covalent structures have a high melting point?
They have lots of strong covalent bonds which require a lot of energy to break
How do metals conduct electricity and heat?
The positive ions are fixed in a sea of delocalised electrons, these electrons are free to move and carry charge/energy
What are two giant covalent structures formed from carbon atoms?
Graphite and Diamond
What is the structure of graphite like?
Each carbon atom bonded to 3 other carbon atoms, layers of hexagonal rings of carbon atoms, weak intermolecular forces between layers and one delocalised electrons per carbon atom
Explain the properties of graphite
Graphite is soft/slippery because there are only weak intermolecular forces between layers which allow the layers to slide over one another and graphite conducts electricity because there is one delocalised electron per carbon atom, the delocalised electrons are mobile charges
What is the structure of diamond like?
All carbon atoms are covalently bonded to four other carbon atoms and no delocalised electrons
What are the properties of diamond?
Very hard, very high melting point and doesn’t conduct electricity as there are no charged particles
What and why are the uses of graphite?
Electrodes because graphite conducts electricity and had a high melting point and lubricant because it’s slippery
Why is diamond used in cutting tools?
It’s very hard
What is a fullerene?
A fullerene is a molecule made of carbon, shaped like a closed tube or hollow ball
What are two fullerenes?
Graphene and C60 (buckminsterfullerene)
What are the properties of the fullerene C60?
Slippery due to weak intermolecular forces, low melting point, spherical, strong covalent bonds between carbon atoms in a molecule and large surface area
What are the properties of graphene?
High melting point due to covalent bonding between carbon atoms and conducts electricity because it had delocalised electrons
Why is graphene useful in electronics?
It’s extremely strong and has delocalised electrons which are free to move and carry charge and it’s only one atom thick as it’s a single layer of graphite
What is a polymer?
Long chain molecules formed from many monomers e.g poly(ethane)
What bond is formed between carbon atoms in polymer molecules?
Covalent bonds
What are the properties of metals?
High melting point, high density, good conductors of electricity, shiny, malleable and ductile
Why are metals malleable?
The atoms are arranged in uniform rows which can slide over one another
Why metals can conduct electricity?
The electrons in metals are charges that can move
What are the properties of non-metals?
Low boiling points, poor conductors of electricity and brittle when solud
What are the limitations of models when representing ionic compounds?
Dot and cross - no lattice structure or ionic bonds, 2D diagram - only shows one layer, doesn’t show formation or ions, 3D diagram - shows spaces between the ions, doesn’t show charges
What are the limitations of models when representing covalent molecules?
Dot and cross - doesn’t show relative sizes of atoms or intermolecular forces, ball and stick - bonds shown as sticks rather than forces, doesn’t show how covalent bonds form
How do you calculate the relative formula mass of a compound?
Add together all the relative atomic masses of the atoms in the compound
What is the empirical formula?
Smallest whole number ratio of the atoms of each elements in a compound, reacting masses or percentage compositions can be used
What are the limitations of models when representing ionic compounds?
What is the molecular formula?
Actual number of atoms of each element in a compound
Describe an experiment to work out the empirical formula of magnesium oxide
Weigh a sample of magnesium, hear the sample in a crucible, weight the mass of magnesium oxide at the end, calculate the mass of oxygen, calculate the moles of magnesium and oxygen using the experimental mass and relative atomic mass and work out the whole number ratio of the number of moles of magnesium to oxygen
What is the law of conservation of mass?
No matter is lost or gained during a chemical reaction
What equation links mass, moles and relative atomic mass?
Mass = moles x relative atomic mass
How can you calculate concentration in g/dm^3?
Concentration = mass / volume
What is the Avogadro constant?
The number of atoms, molecules or ions in one mole of a given substance, the value of the constant is 6.02 x 10^23
What formula links the Avogadro constant, moles and number of particles?
Number of particles = Avogadro constant x Moles
What is a limiting reagent in a chemical reaction?
The chemical that is used up first in a reaction, preventing the formation of more products, an excess of one of the reactants is used to ensure that the other reactant is completely used up
What is metallic bonding?
Forces of attraction between delocalised electrons and nucleu of metal ions
What are alloys?
Mixtures of metals with other elements and different sizes of atoms distort the layers, so they can’t slide over each other, therefore alloys are harder than pure metals
