Lection 11. Chemical elements and their classification Lection 11. Chemical elements and their classification. S-block of IA group of elements. Hydrogen PhD Falfushynska Halina

Periodic Patterns The chemical behavior of elements is determined by its electron configuration Energy levels are quantized so roughly correspond to layers of electrons around the nucleus. A shell is all the electrons with the same value of n. n is a row in the periodic table. Each period begins with a new outer electron shell

Each period ends with a completely filled outer shell that has the maximum number of electrons for that shell. The number identifying the A families identifies the number of electrons in the outer shell, except helium The outer shell electrons are responsible for chemical reactions. Group A elements are called representative elements Group B elements are called transition elements.

Chemical “Families” IA are called alkali metals because the react with water to from an alkaline solution Group IIA are called the alkali earth metals because they are reactive, but not as reactive as Group IA. They are also soft metals like Earth. Group VIIA are the halogens These need only one electron to fill their outer shell They are very reactive. Group VIIIA are the noble gases as they have completely filled outer shells They are almost non reactive.

Four chemical families of the periodic table: the alkali metals (IA), the alkaline earth metals (IIA), halogens (VII), and the noble gases (VIIIA).

Metal: Elements that are usually solids at room temperature Metal: Elements that are usually solids at room temperature. Most elements are metals. Non-Metal: Elements in the upper right corner of the periodic Table. Their chemical and physical properties are different from metals. Metalloid: Elements that lie on a diagonal line between the Metals and non-metals. Their chemical and physical properties are intermediate between the two.

Elements with 1, 2, or 3 electrons in their outer shell tend to lose electrons to fill their outer shell and become cations. These are the metals which always tend to lose electrons. Elements with 5 to 7 electrons in their outer shell tend to gain electrons to fill their outer shell and become anions. These are the nonmetals which always tend to gain electrons. Semiconductors (metalloids) occur at the dividing line between metals and nonmetals.

Cs 133 55 Atomic number = protons and electrons How many protons, neutrons and electrons are found in an atom of 133 55 Cs Atomic number = protons and electrons There are 55 protons and 55 electrons Mass number = sum of protons and neutrons 133 – 55 = 78 There are 78 neutrons

Members of the s-Block Elements Li Be Na K Rb Cs Fr Mg Ca Sr Ra Ba IA IIA IA Alkali metals IIA Alkaline Earth metals

Physical Properties The alkali metals are soft, with low melting and boiling temperatures. They have low densities - Li, Na and K are less dense than water. They have low standard enthalpies of melting and vaporization. They show relatively weak metallic bonding as only one electron is available from each atom. Alkali metals colour flames. The ionic radii of the alkali metals are all much smaller than the corresponding atomic radii. This is because the atom contains one electron in an s level relatively far from the nucleus in a new quantum shell, and when it is removed to form the ion the remaining electrons are in levels closer to the nucleus. The metal thus obtained is 99% pure and is preserved by keeping it wrapped in paraffin wax.

Metallic character High tendency to lose e- to form positive ions Metallic character increases down both groups

Electronegativity Low nuclear attraction for outer electrons Highly electropositive Small electronegativity Group I Li 1.0 Na 0.9 K 0.8 Rb 0.8 Cs 0.7 Fr 0.7

Predominantly ionic with fixed oxidation state Most electropositive metals. Low first I.E. and extremely high second I.E. Form predominantly ionic compounds with non-metals by losing one electron. Fixed oxidation state of +1.

Flame test Li deep red Na yellow K lilac Rb bluish red Cs blue Na+ Cl- (g)  Na (g) + Cl (g) Na(g)  Na* (g) [Ne]3s1 [Ne]3p1 Na*(g)  Na(g) + h (589nm, yellow) Flame test Li deep red Na yellow K lilac Rb bluish red Cs blue HCl(aq) sample

Weak tendency to form complex Complex formation is a common feature of d-block element. e.g. Co(NH3)63+ Co :NH3 H3N: s-block metal ions have no low energy vacant orbital available for bonding with lone pairs of surrounding ligands, they rarely form complexes.

Atomic radii (nm) Ionization Enthapy Group I 1st I.E. 2nd I.E. Li 519 7300 Na 494 4560 K 418 3070 Rb 402 2370 Cs 376 2420 Li 0.152 Na 0.186 K 0.231 Rb 0.244 Cs 0.262 Fr 0.270 Ionization Enthapy Diagonal relationship of lithium with magnesium on the basis of polarizing power, electronegativity and covalent nature

Variation in Melting Points Note: The exceptionally high m.p. of calcium is due to contribution of d-orbital participation of metallic bonding. 10 20 30 40 50 60 250 500 750 1000 1250 Be Mg Ca Sr Ba Li Na K Rb Cs

Occurrence and Extraction These elements are too reactive to be found free in nature. Sodium occurs mainly as NaCI (salt) in sea-water and dried-up sea beds. Potassium is more widely distributed in minerals such as sylvite, KCI, but is also extracted from sea-water. The alkali metals are so reactive they cannot be displaced by another element, so are isolated by electrolysis of their molten salts.

Electrolysis of Lithium chloride A mixture of dry lithium chloride (55%) and potassium chloride (45%) is fused and electrolysed in an electrolytic cell shown in the figure. Potassium chloride is added to increase the conductivity of lithium chloride and to lower the fusion temperature. The cell is operated at a temperature of about 723 K and voltage of 8-9 volts is applied.      At cathode:  Li+ + e- → Li At anode :  2CI- - 2e- → CI2

Basic oxides, hydroxides Li2O LiOH Na2O, Na2O2 NaOH K2O2, KO2 KOH Rb2O2, RbO2 RbOH Cs2O2, CsO2 CsOH Reaction with water: Oxide: O2- + H2O  2OH- Peroxide: O22- + 2H2O  H2O2 + 2OH- Superoxide: 2O2- + 2H2O  2OH- + H2O2 + O2 Strength increase . . - :O:.O: .. .. Super oxide .. .. 2- :O:O: .. .. Peroxide ion

Experimentally and theoretically proved that alkali metals can form covalent diatonic molecule M2. Alkali metals containing approximately 1% of M2. Li2 molecule can exist and does exist, because the binding effect dominates the effect of break and the energy of Li-Li is quite large (25.8 kcal / mol). Among the heteronuclear alkali-metal fermionic species, LiNa is the least reactive, whereas LiCs is the most reactive. For the bosonic species, LiK is the most reactive in zero field, but all species considered, LiNa, LiK, LiRb, LiCs, and KRb, share a universal reaction rate once a sufficiently high electric field is applied. (Phys. Rev. A 84, 062703 (2011)).

Reactions with oxygen Normal Oxide Peroxide Superoxide Formed by Li Na S-block elements are strong reducing agents. Their reducing power increases down both groups. (As the atomic size increases, it becomes easier to remove the outermost electron) S-block elements reacts readily with oxygen. they have to be stored under liquid paraffin to prevent contact with the atmosphere. Normal Oxide Peroxide Superoxide Formed by Li Na K, Rb, Cs

Reaction with hydrogen Reaction with water Reaction with hydrogen M(s)  M+(aq) + e- H2O(l) + e-  OH-(aq) + ½ H2(g) All the IA elements react directly with hydrogen. 2Na(s) + H2(g)  2NaH(s) The reactivity increases down the group. The hydrides are ionic. Although lithium has highly negative Eo, it only reacts slowly with water. This illustrates the importance of the role of kinetic factors in determining the rate of a chemical reaction. The spontaneously inflammable silicone hydride reacts with the oxygen of the air. SiH4 + 2 O2==> SiO2 + 2 H2O     

Reaction with chlorine Reactions of chlorides All the s-block metals react directly with chlorine to produce chloride. 2Na(s) + Cl2(g)  2NaCl(s) All group I chlorides are ionic. All group I chlorides are ionic and readily soluble in water. No hydrolysis occurs.

Reactions of oxides and hydroxides All group I oxides reacts with water to form hydroxides Oxide: O2- + H2O  2OH- Peroxide: O22- + 2H2O  H2O2 + 2OH- Superoxide: 2O2- + 2H2O  2OH- + H2O2 + O2 All group I oxides/hydroxides are basic and the basicity increases down the group.

Reactions of hydrides They all react readily with water to give the metal hydroxide and hydrogen due to the strong basic property of the hydride ion, H:- H:-(s)+ H2O(l)  H2(g)+ OH-(aq) Hydride ions are also good reducing agent. They can be used to prepare complex hydrides such as LiAlH4 and NaBH4 which are used to reduce C=O in organic chemistry.

Solvay process The Solvay process results in soda ash (sodium carbonate (Na2CO3)) from brine (NaCl) and from limestone (as a source of calcium carbonate (CaCO3)). The overall process is: 2 NaCl + CaCO3 → Na2CO3 + CaCl2 1. In the first step in the process, CO2 passes through a concentrated aqueous solution of NaCl and ammonia (NH3). NaCl + CO2 + NH3 + H2O → NaHCO3 + NH4Cl (I) 2. The CaCO3 in the limestone is partially converted to quicklime CaO and CO2: CaCO3 → CO2 + CaO (II) 3. The sodium bicarbonate (NaHCO3) that precipitates out in reaction (I) is filtered out from the hot NH4Cl solution, and the solution is then reacted with the CaO left over from heating the limestone in step (II). 2 NH4Cl + CaO → 2 NH3 + CaCl2 + H2O (III) CaO makes a strong basic solution. The NH3 from reaction (III) is recycled back to the initial brine solution of reaction (I). The NaHCO3 precipitate from reaction (I) is then converted to the final product, Na2CO3, by calcination (160 - 230 C), producing water and carbon dioxide as byproducts: 2 NaHCO3 → Na2CO3 + H2O + CO2 (IV)

Thermal Stability of carbonates and hydroxides Thermal stability refers to decomposition of the compound on heating. Increased thermal stability means a higher temperature is needed to decompose the compound. Li2CO3  Li2O + CO2 ( at 700oC) All other group I carbonates are stable at ~800oC All group I hydroxides are stable except LiOH at Bunsen temperature (lies between 750-950 degrees Celsius).

Uses of s-block compounds Sodium carbonate Manufacture of glass Water softening Paper industry Sodium hydrocarbonate Baking powder Soft drink

Alkali metals in farmacy Lithium stearate is mixed with oils to make all-purpose and high-temperature lubricants Lithium carbonate has a sedative effect. It is highly effective in preventing attacks of depression or mania, by stabilising your chemistry. Potassium bromide, KBr, was used as an antaphrodisiac Potassium permanganate, KMnO4, is an important oxidizing, antiseptic and antidote agent Baking soda (NaHCO3) due to its extremely basic is an especially good antacid and is used in products such as Alka-Seltzer. Important: Children under the age of 6 should not take any antacid medicines unless prescribed by a doctor. Drinking soda with a medicine pill make it dissolve faster once it is swallowed .

Alkali metals Poisoning External exposure to large amounts of Cs-137 can cause burns, acute radiation sickness and even death. Exposure to Cs-137 can increase the risk for cancer because of exposure to high-energy gamma radiation. Internal exposure to Cs-137, through ingestion or inhalation, allows the radioactive material to be distributed in the soft tissues, especially muscle tissue, exposing these tissues to the beta particles and gamma radiation and increasing cancer risk.

Alkali metals analysis Na+ + [Sb(OH)6]  Na[Sb(OH)6] – white crystalline precipitate Na+ + Zn(CH3COO)2 + 3UO2(CH3COO)2 + CH3COO– + 9H2O  NaCH3COOZn(CH3COO)23UO2(CH3COO)29H2O – green-yellow precipitate KCl + NaHC4H4O6  KHC4H4O6 + NaCl – white crystalline precipitate 2K+ + Na+ + [Co(NO2)6]3–  K2Na[Co(NO2)6] – yellow precipitate;

Hydrogen is the simplest of all elements

Production of hydrogen As the reaction between a metal and acid produces hydrogen, we can place this reaction in a flask that is connected to a delivery tube, that will allow hydrogen to pass through it ending up in a water trough, hydrogen will try to escape by bubbling up into the glass jar

Extraction of Hydrogen Zn + 2HCl  ZnCl2 + H2 Al + NaOH + 3H2O  Na[Al(OH)4] + 3/2 H2 2Na + 2H2O  2NaOH + H2 СaH2 + 2H2O  2Ca(OH)2 + H2 С + 2H2O  СO + H2

Properties of hydrogen Colorless: - can’t be see Odorless: - has no small Tasteless: - doesn’t have a taste Gas: - found in gas state, not liquid, or solid Lightest gas: - least density, lighter then air Explosive: - H2 + O2 H2O + energy reactants combine causing an explosion

Chemical properties of Hydrogen Hydrogen is slightly more soluble in organic solvents than in water. It does not usually react with other chemicals at room temperature. Hydrogen reacts with oxygen: 2Н2 + О2  2Н2О; Н2 + hν  2Н; Н2 + О2  2ОН ОН + Н2  Н2О + Н Hydrogen is a good reducing agent: CuO + H2  Cu + Н2О Hydrogen also forms ionic bonds with some metals, creating a compound called a hydride: Ca + H2  CaH2 Hydrogen reacts with non-metals: 3Н2 + N2  2NH3; H2 + Cl2  2HCl

Group 1A – The alkali metals Some facts… 1) These metals all have ___ electron in their outer shell 2) Reactivity increases as you go _______ the group. This is because the electrons are further away from the _______ every time a _____ is added, so they are given up more easily. 3) They all react with water to form an alkali (hence their name) and __________, e.g: Potassium + water potassium hydroxide + hydrogen 2K(s) + 2H2O(l) 2KOH(aq) + H2(g) Words – down, one, shell, hydrogen, nucleus