Flashcards
Periodicity
Cards in this deck (36)
- 1What is the periodic table and what does it do?In the periodic table, elements are placed in order of increasing atomic number
- Elements with the same number of valence electrons (outer shell) are placed vertically in the same GROUP
- Elements with the same outer shell of valence electrons are placed horizontally in the same PERIOD - 2What do group numbers in the periodic table indicate?The number of electrons in the outer shell
-Are numbered from one to eight
Group 1- The alkali metals
Group 7 - The halogens
Group 8 - The noble gases
Transition elements are between groups 2 and 3 - 3What does the period number indicate?The number of shells (main energy levels) in an atom
- 4What is the atomic radius?The atomic radius is the distance from the nucleus to the outermost electron
Since this is hard to measure precisely, its usually defined as half the distance between the nuclei of the two bonded atoms of the same element - 5How does atomic radius differ going down a group?Radius increase, as outermost electron is in a higher energy level and is further from the nucleus
- 6What happens to atomic radius across a period?Radius decreases, as electrons are being added to the same energy level, but the number of protons increases attraction to the energy level closer to the nucleus
- 7What happens to ionic radius going down a group?Anions and cations increase in size down a group, as the outermost level gets further from the nucleus, so there is less attraction
- 8What are cations and what happens to their ionic radius?Positive ions, containing fewer electrons than protons
The electrostatic attraction between the nucleus and the outer most electron is greater, and the ion is smaller that the parent atom
Its also smaller because the number of electrons shells is decreased by one
Across a period, the ions contain the same number of elections (isoelectric), but an increasing number of protons, so the ionic radius decreases - 9What are anions and what happens to their ionic radius?Anions contain more electrons than protons, so are larger than the parent atom
Across a period, size decreases because the number of electrons is the same, whereas the number of protons increases - 10What is periodicity?The repeating pattern of physical and chemical properties shown by different periods
Elements in the same group tend to have similar properties, there is only change across periods
These periodic trends can clearly be seen in the atomic radii, ionisation energies, electronegativities and melting points - 11How do melting points differ across and within periods?The melting points depend on both the structure of the element and the type of attractive forces holding the atoms together
NOBLE GASES: Exist as monoatomic molecules with extremely weak forces of attraction between the atoms
GROUP 1: Melting points decrease down the group as the atoms become larger and the strength of the metallic bond decreases
GROUP 7: The van der walls forces between the diatomic molecules increase down the group, so the melting points decrease - 12What is electronegativity?-Electronegativity is a relative measure of the attraction that an atom has for a shared pair of electrons when it is covalently bonded to another atom
-As the size of the atom decreases, the electronegativity increases, so the value increases across a period and decreases down a group
-The most electronegative elements are
F, N and O - 13What happens to ionisation energy down a group?Values decrease, as the outer electron is further from the nucleus and therefore, less energy is required to remove it
Generally values increase across a period. This is as extra elections are filling the same energy level and the extra protons in the nucleus attract the energy level closer, making it harder to remove an electron - 14What happens to group 1 reactivity down the group?GROUP 1- Increase in reactivity down the group
- They all contain one electron in their outer shell
-Very reactive stored under liquid paraffin to stop them reacting with air
- Lose their outer election to form a metal ion
- Good reducing agents - 15What happens to chemical properties of alkali metals down a group?1. Reactivity increases down a group because the outer electron is successively in higher energy levels and less energy is required to remove them
2. Electronegativity decrease because the size of the atom increases
3. First ionisation energy decreases
4. Atomic radius increases as atoms have increasingly more electrons in shells
5. Ionic radii gets larger, as there is more attraction for the delocalised electron from the positively charged nucleus
6. All bonding is metallic, so less energy is needed to break apart the lattice going down a group, as the nucleus is further from the delocalised election and attraction becomes weaker - 16Why are alkali metals called alkali metals?Called alkali metals as they all react with water to from an alkali solution of the metal hydroxide and hydrogen gas
(also react with chlorine/bromine/ iodine to from ionic salts) - 17What happens to the reactivity of the halogens down a group?Halogens get less reactive going down the group
-React by gaining one for electron to from a halide ion
-Good oxidising agents - 18What happens to the chemical properties of the halogens down the group?1. Reactivity decreases because the outer shells is increasingly at higher levels and therefore further from the nucleus
2. There are more electrons between the nucleus and the outer shell, decreasing the attraction for an extra nucleus
3. Electronegativity decreases, as the size of the atom increases
4. Nuclear charge increases (but is balanced by the increase in shielding)
5. Van der walls forces get stronger, meaning more energy is needed to break forces between the molecules and the melting point is higher - 19What happens to the oxidising nature of the halogens down a group?Cl2 is stronger oxidising agent than Br2 (so can remove bromide ions in solution to form chloride ions and bromide)
Both Cl2 and Br2 can oxidise iodide ions to form iodine - 20How do you test for a halide ion?The presence of a halide ion in solution can be tested using SILVER NITRATE
The silver ions in the solution react with halide ions to form a precipitate of silver halide - they are distinguishable by colour
They react with light to form a silver metal
Ag+ (aq) + X- (aq) --> Agx (s) --light--> Ag (s) + 1/2 X2
AgCl - White
AgBr- Cream
AgI- Yellow - 21What happens across period 3 using physical properties of metals to distingusih? (metal to non-metal elements)Metals tend to be shiny, good conductors of heat and electricity
-Sodium, magnesium and aluminium fit this
- Silicon is a semi-conductor (METALLOID) , meaning it contains some metallic qualities and not others
- Phosphorous, chlorine, sulfur and argon are non- metals - 22What happens to the elements across period 3 using chemical properties to distinguish (Metals to non-metals)Metal oxides tend to be basic, non-metals oxides more acidic
-Sodium oxide and magnesium oxides are both basic and react with water to form hydroxides
-Aluminium is a metal, but its oxide is atmospheric (can be wither basic or acidic, depending on whether it reacts with a metal or base)
- The remaining 3 elements in period 3 have acidic oxides - 23What happens to elements when going across period 3?- ELECTRONEGATIVITY increases, as there is an increase in nuclear charge, but no significant change to shielding
-SHIELDING is constant, as the atoms in the same period have the same number of inner shells
-NUCLEAR CHARGE increases, so this makes an increase in FIRST IONISATION ENERGY
-ATOMIC RADIUS decreases - 24What happens to melting points across period three?MELTING POINTS increase from Na to Al, as bonding involved is metallic and for 3 main reasons
1. Electrostatic attraction is greater between delocalised electrons and the +ve ion
2. There are more delocalised electrons per atom
3. As you go down the group, ions get smaller, meaning delocalised electrons are more attracted to the nucleus
SILICONE - has a giant covalent structure, creating a huge jump in mpt, as covalent bonds need to be broken
PHOSPHOROUS - a sharp decrease again, as its covalent molecular structure only contains easy to breaks VDWs
SULPHUR- sees an increase in mpt, as has a much higher Mr to phosphorous
- The last two in the period have reducing Mr's, meaning lower mots - 25What is the nature of the oxides of the period 3 elements?Oxides of Na, Mg and Al are all ionic
- This accounts for high mpts. and electrical conductivity when molten
Silicon dioxide has a diamond-like macromolecular structure, with a high bpt.
The others have small differences in electronegativities with oxygen, resulting in simple covalent molecular structures and low mpts. bpts. - 26What is the acid/ base nature of the period 3 oxides?The acid-base properties of the oxides are also linked to their structure - the oxides of electropositive elements are very basic and form alkaline solutions (Na2O and MgO)
The ampoteric nature of Al2O3 means it can act as acid or base, seen in reactions with HCl and NaOH
Silicon dioxide acts as a weak acid, not reacting with water, but forms silicon silicate with NaOH
The oxides of P, S and Cl are all strongly acidic - 27What is the nature of melting and boiling points for the chlorides of the 3rd period?Physical properties of the chlorides are related to structure - the same as the oxides
NaCl and MgCl2 are ionic, and have high melting points
Unlike silicon dioxide, silicon tetrachloride has a simple molecular structure, which is held together by weak VDWs, resulting in low melting/boiling points - 28What happens to the period 3 chlorides in reactions with water?NaCl dissolves in water to give a neutral solution
MgCl2 is slightly acidic with water
All the others react vigourously with water to produce acidic solution of hydrochloric acid, together with fumes of hydrogen chloride - 29Define transition elementAn element that possesses an incomplete d sub level in one or more of its oxidation states
- 30What are the exceptions of transition elements in the first row of the d- block?1. Scandium is not a typical transition metal, as its common ion Sc3+ has no d electrons
2. Zinc is not a transition metal, as it contains a full d subshell in all its oxidation states - 31What are the characteristical properties of the transition elements?1. VARIABLE OXIDATION STATES
2. COLOURED COMPLEXES
3. COMPLEX IONS - 32What is meant by variable oxidation states in transition elements?1. VARIABLE OXIDATION STATES -The 3d and 4s subshells have very similar energy. When transition metals loose electrons, they loose them from the 4s first. All transition metals can show an oxidation state of 2+ (some 3+ and 4+), as ionisation energies are such that up to 2 d electrons can be lost
Fe3+/ Mn4+
The Mn 4+ ion is rare and in the higher oxidation states, the element is usually found, not as a free metal ion, but covalently bonded, or as an oxyanion (MnO4-) - 33What is meant by coloured complexes in transition elements?In the free ion, the 5 d orbitals are degenerate (of equal energy)
They do however split into 2 distinct levels in complexes when ligands attach to the transition metal
The energy difference between the levels corresponds to a different wavelength/ frequency in the visible spectrum
When light falls on the complex, energy of a particular wavelength is absorbed and electrons are excited from a lower level to a higher level
(we see the colour NOT absorbed)
Cu+ = 3d10 = colourless
Cu2+ = 3d9 = blue - 34What is meant by complex ions in transition elements?Complex ions consist of a transition metal surrounded by ligands
Ligands are natural molecules or anions which contain a non-bonding (lone pair) of electrons
Ligands form from dative covalent (co-ordinate) bonds to transition metals
A common ligand is water, but most transition metal ions exist as hexahydrated complex ions in aqueous solutions
Ligands can be replaced by other ligands
H2O: = Aqua
:NH3 = Ammine
:Cl- = Chloro
:CN- = Cyano - 35What factors affect the colour of a transition metal?1. TYPE OF METAL:
Different metals have different numbers of electrons and different proton numbers (this attracts them to the nucleus)
2. TYPE OF LIGAND:
Different ligands cause different amounts of splitting of the orbitals
3. OXIDATION STATE OF THE METAL:
As will have different numbers of electrons
Cu+ = 3d10 = colourless
Cu2+ = 3d9 = Blue - 36Name 5 catalysts and what they are used for1. MnO2 - In the decomposition of H2O2
2. V2O5 - In contact process for production of H2SO4 (converting SO2 --> SO3)
3. Fe - in the haber process (N2 + 3H2 --> 2NH3)
4. Nickel - In hydrogenation of alkenes, used in margarine production
5. Pt and Pd - Used in catalytic converters
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- IB Chemistry Flashcards on Periodicity, created by P H on 27/01/2015.
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