RoshChem The Periodic Table Chemistry Units 1&2 Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) www.RoshChem.com info@RoshChem.com 0433 019 767 [Date] 97 Chemistry The Periodic Table Units 1 & 2 Dmitri Mendeleev produced a table based on atomic masses and arranged elements 'periodically' with elements having similar properties under each other. Mendeleev proposed periodic law: The properties of elements vary periodically with their atomic weights. Mendeleev`s periodic table was the base for the modern periodic table. Dmitri Mendeleev is known as the father of the periodic table of elements Modern periodic table Elements are arranged in order of increasing atomic number (the number of protons in the nucleus). Consists of 18 columns (groups) and 7 rows (periods), with a double row of elements below that. The table can also be split into four rectangular blocks: the s-block to the left, the pblock to the right, the d-block in the middle, and the f-block below that. Elements in the periodic table are grouped as metals, metalloids and non-metals. The metalloids separate the metals and non-metals on a periodic table. Also, many periodic tables have a stair-step line on the table identifying the element groups. The line begins at boron (B) and extends down to polonium (Po). Elements to the left of the line are considered metals. Elements just to the right of the line exhibit properties of both metals and non-metals and are termed metalloids or semimetals. Elements to the far right of the periodic table are non-metals. The exception is hydrogen (H); at ordinary temperatures and pressures, hydrogen behaves as a nonmetal. Metals Most elements are metals. Metals exhibit the following properties: • usually solid at room temperature (mercury is an exception) • high lustre (shiny) • metallic appearance • good conductors of heat and electricity • malleable (can be bent and pounded into thin sheets) • ductile (can be drawn into wire) • corrode or oxidise in air and seawater Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) www.RoshChem.com 0433 019 767 Page 2 of 9 FOR INDIVIDUAL PERSONAL NON-COMMERICAL USE ONLY. NOT TO BE SOLD OR PROVIDED TO STUDENTS BY THIRD PARTIES. Mendeleev’s periodic table Chemistry The Periodic Table Units 1 & 2 usually dense (exceptions include lithium, potassium, and sodium) • may have a very high melting point • readily lose electrons Non-metals Non-metals exhibit very different properties from metals. Non-metals display some or all of the following characteristics: • dull appearance • usually brittle • poor conductors of heat and electricity • usually less dense compared to metals • usually, a low melting point of solids, compared with metals • tend to gain electrons in chemical reactions Metalloids or Semimetals Metalloids have some of the properties of metals and some nonmetallic characteristics. • dull or shiny • usually conduct heat and electricity, though not as well as metals • often make good semiconductors • often exist in several forms • often ductile • often malleable • may gain or lose electrons in reactions Why are element properties periodic? The arrangement of electrons in atoms is responsible for many properties such as melting temperature, electrical conductivity, and formulas of compounds formed. The outer-shell electronic configuration of an atom is important as these electrons involve in making chemical bonds. Similar electronic configurations occur regularly as the atomic number of atoms increases; this causes periodicity in the chemical properties of elements. Eg: group 1 elements (Li, Na, K, Rb ) show similar chemical properties as they all have similar electronic configurations. Eg: Li 1s2 2s1 Na 1s2 2s2 2p6 3s1 K 1s2 2s2 2p6 3s2 3p6 4s1 Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) www.RoshChem.com 0433 019 767 Page 3 of 9 FOR INDIVIDUAL PERSONAL NON-COMMERICAL USE ONLY. NOT TO BE SOLD OR PROVIDED TO STUDENTS BY THIRD PARTIES. • Chemistry The Periodic Table Units 1 & 2 Eg: group - Li 1s2 2s1 Na 1s2 2s2 2p6 3s1 K 1s2 2s2 2p6 3s2 3p6 4s1 one valence electron Group number Group name Number of valence electrons 1 Alkali metals 1 2 Alkali earth metals 2 13 Boron group 3 14 Carbon group 4 15 Pnictogens or nitrogen group 5 16 chalcogens 6 17 Halogens 7 18 Noble gases 8 (except He, which has 2 valence electrons) Because elements in the same group have the same number of valance electrons, elements in the same group have similar chemical properties. Alkali metals (except hydrogen): relatively soft metals highly react with water and oxygen. Halogens: all are coloured and highly reactive Noble gases: They have a very stable electron arrangement: helium and neon have full outer shells, and the other members of this group have a stable octet of valence electrons (eight electrons). As noble gases have a stable electronic configuration, they do not tend to lose or gain electrons. This means that they have very low reactivity. Periods The periodic table consists of 7 periods. Each period contains elements with electrons in the same outer shell. The number of the period is the same as the number of the outer shell. Eg: Mg- Period 3 1s2 2s2 2p63s2 Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) S- Period 3 1s2 2s2 2p63s2 3p4 www.RoshChem.com 0433 019 767 Page 4 of 9 FOR INDIVIDUAL PERSONAL NON-COMMERICAL USE ONLY. NOT TO BE SOLD OR PROVIDED TO STUDENTS BY THIRD PARTIES. Groups The periodic table consists of 18 groups. Groups contain elements with similar outer shell electronic configurations. Chemistry The Periodic Table Units 1 & 2 s block- consisting of group 1 and 2 elements. These elements have filled or half-filled s-subshell as the highest energy subshell. p block- consists of groups 13-18 elements. These elements have s2p1-s2P6 outer shell configuration. d block- consisting of transition metals and located between s and p blocks. In these elements, dsubshells are progressively being filled. These elements have d1s2-d10s2 outer shell configuration. f block- consists of lanthanides and actinides. In these elements, f-subshells are progressively being filled. Lanthanides- set of 14 elements with atomic numbers 57-71. In these elements, 4f-subshells are progressively being filled. Actinides- elements with atomic numbers 89-103. In these elements, 5f-subshells are progressively being filled. Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) www.RoshChem.com 0433 019 767 Page 5 of 9 FOR INDIVIDUAL PERSONAL NON-COMMERICAL USE ONLY. NOT TO BE SOLD OR PROVIDED TO STUDENTS BY THIRD PARTIES. Blocks of elements The periodic table consists of four main blocks Chemistry The Periodic Table Units 1 & 2 Of the 118 elements in the periodic table, many exist in very small amounts on earth. Over 40 elements have been identified as being ‘endangered.’ This is because the use of these elements in industry and medicine has increased. But, there is very little recycling and recovery of these metals. Examples of some endangered elements Mn, Sr, Zn, Ga, Ge, As, W, U, Sb, Bi, Os, Pt , Pd Critical elements are elements that are heavily relied on for industry and society in areas such as renewable energy, electronics, food supply and medicine. Elements may be considered critical if i. Only small deposits are available on earth, and these are endangered elements. Eg: Os, Pt , Pd ii. The supply of these elements is centred in places of war and conflict (conflict elements). Conflict elements, such as tin, gold, tungsten and tantalum, are essential in mobile phone production. These elements are mined in areas of war and conflict, and they routinely use child labour in their mining, which makes their use non-sustainable. iii. The recycling of these metals is little or, in some cases, not at all, so reserves are being used up. Eg: the rare earth elements (Lanthanides) – the current rate of recycling is less than 1% iv. Deposits of these metals are concentrated in a small number of countries, and so the supply is at risk (critical raw materials) Eg: deposits of W, Sb, Ge, Ga and In are concentrated in China. Deposits of Pt, Pd, Rh, Ru and V are concentrated in South Africa. v. The use of these elements has largely increased due to the expansion of new technologies. Eg: Helium in medical technologies where ultra-low-temperature liquid helium is used to cool instruments and Phosphorous to make fertilisers. Recycling of some critical elements 1. Recycling of old mobile phones and other electronic waste. Eg: During the 2020 Tokyo Olympics, 79,000 tonnes of old mobile phones and other electronic waste were recycled to recover precious metals, and these were used to make gold, silver and bronze medals. 2. Recovery of phosphorous from human urine to create fertilisers. Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) www.RoshChem.com 0433 019 767 Page 6 of 9 FOR INDIVIDUAL PERSONAL NON-COMMERICAL USE ONLY. NOT TO BE SOLD OR PROVIDED TO STUDENTS BY THIRD PARTIES. Critical elements Chemistry The Periodic Table Units 1 & 2 Electronic configuration Eg: period 3 In Period 3 of the Periodic Table, the 3s and 3p orbitals are filling with electrons. The abbreviated electronic structures for the eight elements are shown below. In each case, [Ne] represents the complete electronic structure of a neon atom. Na [Ne] 3s1 P [Ne] 3s2 3p3 Mg [Ne] 3s2 S [Ne] 3s2 3p4 Al [Ne] 3s2 3p1 Cl [Ne] 3s2 3p5 Si [Ne] 3s2 3p2 Core charge/Effective nuclear charge It is the attractive force of the nucleus of an atom on the valance electrons. Group The outer shell electron of an atom does not feel the full attraction by its protons due to the presence of inner shell electrons. So, we call 1 2 outer shell electrons experiencing a core charge. 13 14 Core charge= atomic number – all the inner shell electrons 15 16 Cl= 17- 10= +7(1s2 2s2 2p63s2 3p5) 17 18 Li= 3-2= +1 Ar [Ne] 3s2 3p6 Core charge +1 +2 +3 +4 +5 +6 +7 +8 Trends in the change of core charge across a period and down a group The trend in core charge Remains constant, but the outer shell electrons are held less strongly as they are further from the nucleus. Increases, so valence electrons are more attracted to the nucleus. Down a group Across a period Electronegativity Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to francium which is the least electronegative at 0.7. Trend electronegativity Down a group Decreases Across a period Increases Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) in Explanation The core charge stays constant, and the number of shells increases down a group. Therefore, valence electrons are less strongly attracted to the nucleus as they are further from the nucleus. So, electronegativity decreases. The number of occupied shells in the atom remains constant, but the core charge increases. So, valence electrons become more strongly attracted to the nucleus. So, electronegativity increases. www.RoshChem.com 0433 019 767 Page 7 of 9 FOR INDIVIDUAL PERSONAL NON-COMMERICAL USE ONLY. NOT TO BE SOLD OR PROVIDED TO STUDENTS BY THIRD PARTIES. Trends in Properties of elements in the periodic table Chemistry The Periodic Table Units 1 & 2 The trend in atomic Explanation radii Down a group increase The core charge stays constant, and the number of shells increases down a group. So atomic radii increase. Across a decreases The number of occupied shells in the atom remains period constant, but the core charge increases. So valence electrons become more strongly attracted to the nucleus. So atomic radii decrease. First ionisation energy The first ionisation energy is the energy required to remove the most loosely held electron from a gaseous atom to produce a gaseous ion with a charge of 1+. M(g)→ M+(g) + e • • Ionisation energy decreases down a group. Ionisation energy increases across a period from left to right. Explaining the pattern First, ionisation energy is governed by: The charge on the nucleus, the distance of the outer electron from the nucleus and the amount of screening by inner electrons. Across a period For example, in the whole of period 3, the outer electrons are in the 3rd energy level. These are all the same sort of distances from the nucleus and are screened by the same electrons in the first and second levels. The major difference is the increasing number of protons in the nucleus as you go from sodium across to argon. That causes greater attraction between the nucleus and the electrons, and so increases the ionisation energies. Down the group Going down the group, the trend is that ionisation energy decreases because as you go down the group, you are removing an electron from a higher energy level which is further from the nucleus. The outer electrons are more screened by the inner electrons; therefore, the attraction between the nucleus and the outer electrons is reduced. Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) www.RoshChem.com 0433 019 767 Page 8 of 9 FOR INDIVIDUAL PERSONAL NON-COMMERICAL USE ONLY. NOT TO BE SOLD OR PROVIDED TO STUDENTS BY THIRD PARTIES. Atomic radii The radius of an atom can only be found by measuring the distance between the nuclei of two touching atoms and then halving that distance. Chemistry The Periodic Table Units 1 & 2 Reactivity of metals Reactivity increases down a group. – Metals react by removing electrons, and the reactions become easier as the energy needed to form positive ions falls. This is due to the decrease in ionisation energy as you go down the group, so you can remove electrons easily. Group 1 and 2 metals react with water to produce metal hydroxide and hydrogen gas. 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) Group 1 metals are more reactive than group 2 metals The reactivity of metals increases down a group as the number of shells are increasing, and becoming easier to remove electrons The reactivity of metals decreases across the period as the core charge increases and becoming difficult to remove electrons Eg: sodium with water: react vigorously. Energy release can melt sodium, which fizzes and floats on the water's surface Potassium with water: react violently, making cracking sounds. Energy release can ignite hydrogen gas produced. Calcium with water: slow reaction at room temperature. Reactivity of non-metals Non-metals electrons react by gaining The reactivity of non-metals decreases going down a group as it becomes difficult to attract electrons when there are more shells The reactivity of non-metals increases across a period as it becomes easy to attract electrons with the greater core charge. Summary of Trends in Properties of elements in the periodic table Property Core charge Electronegativity Atomic radius First ionisation energy Reactivity of metals Reactivity of non-metals Down a group remain constant decrease increases decreases increases decreases Dr. Roshani Peiris PhD (Monash University), Grad. Chem. (1st class Hons.) Across a period increases increases decreases increases decreases Increases www.RoshChem.com 0433 019 767 Page 9 of 9 FOR INDIVIDUAL PERSONAL NON-COMMERICAL USE ONLY. NOT TO BE SOLD OR PROVIDED TO STUDENTS BY THIRD PARTIES. Metallic character Increase down a group Decrease across a period- Na, Mg, Al are metals Si is a metalloid and P, S and Cl are non-metals.
