atomic structure and the periodic table Flashcards
revision
what is an atom
an atom is the smallest part of an element that can exist
what is an element
an element is a substance of only one type of atom
how are the elements listed and approximatley how many are there
they are listed in the periodic table. There are approximatley 100
elements can be classified in to two groups based on their properties. what are these called
metals and non-metals
elements may combine through chemical reaction to from new products. what are these new substances called
compounds
what is a compound
two or more elements combined chemically together in fixed proportions which can be represented by formulae
do compounds have the same properties as their constutuent elements
no they have diffrent properties
what is a mixture. does it have the same chemical properties as its constitient materials
a mixture consists of two or more elements or compounds not chemically combined together. it des have the same chemical properties
what are the methords through which mistures can be seperated (there are five)? do these involve chemical reactions
filteration. crysterlisation, simple distilation, fractional distilation and chromotography. they do nto invole chemical reactions
descrive and explain simple distilaion
simple distilation is used to seperate liquid from a soloution - the liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contraty to evaporate, we get to keep the liquid.
describe and explain crystallisation/evaporation
evaporation is a tequnice for seperation of a solid dissolved in a solvent from a solvent (e.g salt from h2o)
The soloution is heated until all the solvent evapprates. the solids stay in the vessel.
crystalisation is similar but we only remove some of the solvant by evaporating to form a saturated soloution (the one where no more solids can be dissolved). Then we cool down the solution. As we do it, the solids start to crystalise, as it becomes less soluble at lower temprature. The crysatls can be collected and seperated from the solvant via filteration.
Describe and explain factional distilation
fractional distilation is a technique for seperation of a mixture of liquids. It works when liquids have diffrent boiling points.
The apparatus is similar to the one of simple distilation apparatus, with the additional fractional colounm placed on top of the heated flask.
The fractionating comloun contatin glass beads. It helps to serperate the compounds. In the indistry, mixtures are repeatedly condensed and vapourised. The column is hot at the bottom and cold at the top. The liquids will condencse at the diffrent heights of the column.
describe and explain filteraiton
Filtration is used to separate an insoluble solid is suspended in a liquid. The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper. The filtrate is the substance that comes through the filter paper. Apparatus: filter paper + funnel.
describe and explain chromatograhy
Chromatography is used to separate a mixture of substances dissolved in a solvent. In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent. The bottom of the paper has to be in contact with the solvent. The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).
what is a sperating funnel
A separatory funnel is an apparatus for separating immiscible liquids. Two immiscible liquids of different densities will form two distinct layers in the separatory funnel. We can run off the bottom layer (the liquid with greater density) to a separate vessel.
describe the plum-pudding model
The atom is a ball of positive charge with negative electron embedded in it.
describe the Bohr/nuclear model and hot it came about
The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) – it came about from the alpha scattering experiments
later experiments led to the discovery of smaller, positive prticles in the nucleus; what are these particles called?
protons
what did the work of James Chadwick provide evidence for
the existance of neutrons in the nucleus
describe the structure of an atom
the atom has a small central nucleus (made up of protons and neutrons) around with there are electrons
state the relative masses and relative charges of the proton, nreutron and electron
masses: 1,1,very small ; charges: 1,0,-1
explain why atoms are electrically neutral
they have the same number of electrons and protons
what is the radius of an atom
0.1 nm
what is the radious of a nucleous and what is ti compared to that of the atom
1 x 10^ -14 m and 1/10000
what name is given to the number of pretons in the nucleus
atomic number
atoms of the same element have the same number of which particle in the nucleous
protons
where is the majority of the mass of an atom
the nucleous
what is the mass numebr
the total number of protons and neutrons
how does one caculate the number of neutrons using mass number and tomic number
subtract the atomic number from the mass number
what is an isotope? Do isotopes of a certain element have the same chemical properties?
atoms of the same element (same proton num) that have a diffrent number of neutrons
They have the same hemical properties as they have the same electronic structure
what is the relative atomic number
The average mass value wich takes the mass and abundance of the isotopes of an element into account, on a scale where the mass of 12C is 12.
Give the electronic configurations of He (2), Be (4), F (9), Na (11), and Ca (20) to demonstrate how shells are occupied by electrons
2
2,2
2,7
2,8,1
2,8,8,2
what are ions
Ions are charged particles. They are formed when atoms lose electrons (positive ions) or gain (negative ions) electrons. E.g. sodium positive ion, Na + , has an electronic configuration of 2,8 (same as Ne). An atom of sodium has lost one electron.
what is fromed when a metals reacts with a non-metal
An ionic compound (made of positive and negative ions).
what is fromed when a non-metal reacts with a non-metal
A molecular compound containing covalently bonded atoms. Atoms share electrons, as opposed to transferring electrons between each other (cf. ionic compounds).
explain the following: solute, solvent, solution, misciuble, immiscible, soluble, insolible
A solute is a substance that is dissolved in a solvent. Together, they form a solution. Miscible refers to the substances (particularly liquids) that mix together, e.g. water and alcohol. Water and oil are immiscible, i.e. they do not mix. Soluble refers to the substance that can be dissolved in a solvent, e.g. salt in water. Insoluble substance won’t dissolve in a particular solvent.
the columns of the periodic table are called?
groups
the rows of the periodic table are called?
periods
are elements in the same similar or diffrent
They may have similar chemical properties, as they have the same number of outher shell electorns
in the terms of energy levels, what are the diffrences between elements of the same period
they have the same number of energy levels
electrons occupt particular energy levels, with each electon in an atom at a particular energy level; which avalible ebergylevel do electrons occupy?
the lowest avalible energy level
The elements of Group 0 are more commonly known as…?
the nobal gases
What makes the periodic table periodic?
Similar properties of elements occur at regular intervals
Elements in the same group have the same number of electrons in their outer shell; what does this tell us about their chemical properties?
They have similar chemical properties
In terms of shells, what is the difference between elements in the same period?
They have the same number of shells
What change in shell number is seen as one moves down a group?
The number of shells increases
Early periodic tables were incomplete and elements were placed in inappropriate groups if what was to be followed?
The strict order of atomic weights
Knowledge of what made it possible to explain why the order based on atomic weights was not always correct?
Isotopes
Mendeleev overcame some problems with the table by doing what? He also changed the order of some elements based on what?
Leaving gaps; atomic weights
The majority of elements are…?
Metals
Elements that react to form positive ions are…?
Metals
Elements that do not form positive ions are…?
Non-metals
Elements in Group 1 are known as…?
The alkali metals
State three characteristics of the Alkali
All have one electron in their outer shell; have low density; are stored under oil (to prevent reactions with oxygen or water); are soft (can be cut with knife).
How do Group 1 elements react with non-metals? Why are these reactions similar for the different Group 1 elements
They form ionic compounds which are soluble white solids which form colourless solutions – they all have one electron in their outer shell.
How do Group 1 elements react with water?
They release hydrogen and form hydroxides which dissolve to form alkaline solutions; react vigorously with water fizzing and moving around on the surface of the water.
How does the reactivity change moving down Group 1? Why?
Reactivity increases as the atoms get larger and the distance between the nucleus and the outer electrons increases and thus attraction from the nucleus decreases, allowing them to more easily lose electrons
State five characteristics of Group 7
- 7 electrons in outer shell - Coloured vapours - Diatomic molecules - Form ionic salts with metals - Form molecular compounds with non-metals
State Group 7 elements and their states of matter.
- Fluorine, F. F 2is a pale yellow gas. - Chlorine, Cl. Cl 2is a pale green gas. - Bromine, Br. Br 2is dark brown liquid - Iodine, I. I 2is a grey solid.
State three changes that occur in Group 7 as one moves down the group
- Higher relative molecular mass - Higher melting and boiling point - Less reactive – less easily gain electrons
A more reactive halogen displaces a less reactive one from an aqueous solution of its salt; write the equations and state the colour change seen when chlorine reacts with sodium bromide and when chlorine/bromine reacts with sodium iodide.
Cl 2+ 2 NaBr → Br 2+ 2 NaCl, or Cl 2+ 2Br – → Br 2+ 2 Cl – ; in this reaction, an orange colour of Br 2would appear Cl 2+ 2 NaI → I 2+ 2 NaCl, or Cl 2+ 2I –→ I 2+ 2 Cl –Br 2+ 2 NaI → I 2+ 2 NaBr, or Br 2+ 2I –→ I 2 + 2 Br – ; in these two reactions, a brown colour of I 2would appear
A more reactive halogen displaces a less reactive one from an aqueous solution of its salt; explain the trend in reactivity of halogens in these reactions
Reactivity decreases down the group. As we go down the group, the atoms get larger, so an incoming electron will be less tightly held by the attractive forces from the nucleus. That’s why Cl 2displaces Br –and I – .
Compare Group 1 metals and transition metals
Group 1 metals and transition metals are heat and electricity conductors. They are shiny when polished and form ionic compounds with non metals. Transition metals have higher densities and higher melting points than Group 1 metals. They are less reactive and harder than Group 1 metals.
State three common characteristics of transition metals
- Ions with different charges - Coloured compounds - Catalytic properties
What is a catalyst?
A catalyst is a chemical substance that increases the rate of a chemical reaction. It is not used up over the course of the reaction.
State the colours of flames observed when lithium, sodium, and potassium burn in oxygen
Crimson-red, Li Yellow-orange, Na Lilac, K
Describe the properties of noble gases. Discuss the trend in boiling point down the group.
Non-metals, gases, low boiling points, unreactive (full outer shell; they don’t easily accept or lose electrons). The boiling point increases down the group, as the atoms get heavier.
