Metals, Non-metals & Metalloids – Recap ലോഹങ്ങൾ · അലോഹങ്ങൾ · ഉപലോഹങ്ങൾ
This chapter is about five non-metals (അലോഹങ്ങൾ): hydrogen, carbon, nitrogen, oxygen and chlorine. Before meeting them one by one, this page makes sure you can tell a metal (ലോഹങ്ങൾ) from a non-metal and a metalloid (ഉപലോഹങ്ങൾ). You will find where each kind sits in the periodic table and fill in Table 7.1. You will recall from Chapter 2 the electron shells and the families (മൂലക കുടുംബങ്ങൾ) of the five elements. From Chapter 3 you will recall how atoms share electrons to make covalent bonds and diatomic molecules such as H₂ and N₂. Last comes a first look at allotropes, the different forms of one element. Nothing is assumed.
- Atoms have a nucleus with protons and neutrons, and electrons in shells around it (Chapter 1).
- If you can already write the electron configuration of chlorine, say which group it is in, and draw the bond in N₂, do the sorters and the quiz, then go to page 2.
1. Metals, non-metals and metalloids
About three quarters of all elements are metals: iron, copper, aluminium, gold, sodium. They are shiny, can be beaten into sheets and drawn into wires, and carry heat and electricity well. Non-metals are fewer, but they make up nearly all of the air (nitrogen, oxygen, argon, carbon dioxide) and most of your body (oxygen, carbon, hydrogen, nitrogen). Solid non-metals such as sulphur are dull and brittle: they break instead of bending. A few elements, the metalloids, have some properties of each. Silicon looks shiny like a metal but is brittle, and it conducts electricity only a little. That is why it is used in computer chips.
| Property | Metals ലോഹങ്ങൾ | Non-metals അലോഹങ്ങൾ | Metalloids ഉപലോഹങ്ങൾ |
|---|---|---|---|
| Shine (lustre) | shiny when freshly cut or polished | usually dull (graphite and iodine shine a little) | often shiny, like a metal |
| State at room temperature | solids (mercury is a liquid) | gases (hydrogen, nitrogen, oxygen, chlorine), one liquid (bromine) or solids (carbon, sulphur, phosphorus, iodine) | solids |
| Hammering | flatten into sheets: malleable | solids break: brittle | brittle |
| Pulling into wires | possible: ductile | not possible | not possible |
| Heat and electricity | good conductors: high thermal conductivity (താപചാലകത) and electrical conductivity (വൈദ്യുതചാലകത) | poor conductors (graphite is the exception: it conducts electricity) | conduct a little (semiconductors) |
| Sound when struck | ring (sonorous): temple bells | no ring | no ring |
| Electrons in reactions | give away outer electrons and form positive ions (Na⁺, Mg²⁺) | take electrons (Cl⁻, O²⁻) or share them in covalent bonds | usually share electrons |
A virtual test bench: choosing another sample clears the bench. In a real school lab, hammering is done on a sample wrapped in paper, and only with low-voltage cells.
Graphite, a form of carbon, is a non-metal that conducts electricity. That is why the centre rod of a dry cell is graphite (page 5). Diamond, another form of the same carbon, is the hardest natural substance and does not conduct at all. Mercury is a metal but a liquid. Sodium is a metal soft enough to cut with a knife. So decide by looking at several properties together, and above all by the position in the periodic table.
2. Where they sit in the periodic table
The periodic table sorts the three kinds neatly. Metals fill the left side and the middle: groups 1 and 2, all the transition elements (groups 3–12), and the lower parts of groups 13–16. Non-metals sit at the top right. Metalloids form a thin diagonal band between them along the staircase line: boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb) and tellurium (Te). Hydrogen is the odd one out. It sits at the top of group 1 because it has one outer electron, but it is a non-metal gas, not an alkali metal.
Tap an element, then tap the column it belongs to. Tap a placed element to send it back. The textbook (page 133) asks for a few examples of each kind; here are eighteen.
Table 7.1 (പട്ടിക 7.1). Any correct examples are right in your notebook; the chapter's own examples are Na, Mg, Al, Fe, Cu, Zn · H, C, N, O, S, Cl · B, Si, Ge, As, Sb, Te.
3. Electron configurations of H, C, N, O and Cl
In Chapter 2 you wrote the electron configuration (ഇലക്ട്രോൺ വിന്യാസം) of an atom by filling its shells: at most 2 electrons in the first shell and 8 in the second; in the first 20 elements the third shell also takes up to 8. The number of shells gives the period. For these main-group elements the outermost electrons give the group: 1 or 2 outer electrons → group 1 or 2; 3 to 8 outer electrons → group 10 + that number. Elements of a group form a family (മൂലക കുടുംബങ്ങൾ) with similar properties.
Valency (സംയോജകത) is the combining power of an atom. For these non-metals it is the number of electrons the atom still needs to fill its outer shell: hydrogen needs 1 (to reach 2, like helium), carbon 4, nitrogen 3, oxygen 2 and chlorine 1 (to reach 8). That is why water is H₂O, ammonia NH₃ and methane CH₄.
4. Covalent bonds and diatomic molecules (a recap of Chapter 3)
Non-metal atoms reach a full outer shell by sharing electrons. A shared pair of electrons holds the two atoms together: a covalent bond (സഹസംയോജകബന്ധനം). One shared pair is a single bond (ഏകബന്ധനം), two pairs a double bond (ദ്വിബന്ധനം) and three pairs a triple bond (ത്രിബന്ധനം). Hydrogen, nitrogen, oxygen and chlorine gases are each made of molecules with two atoms: they are diatomic molecules (ദ്വയാറ്റോമിക തന്മാത്ര).
5. A first look at allotropes
The same atoms can be arranged in different ways. Carbon atoms joined to four neighbours in a 3-D network make diamond. Carbon atoms joined to three neighbours in flat sheets make graphite, the “lead” of your pencil. Sixty carbon atoms closed into a hollow ball make a fullerene. These are not mixtures or compounds: each is pure carbon. Different forms of the same element with different physical properties are called allotropes (രൂപാന്തരങ്ങൾ), and the existence of such forms is allotropy (രൂപാന്തരത്വം). Oxygen has allotropes too: ordinary oxygen O₂ and ozone O₃ (page 8). Page 5 explores the allotropes of carbon in detail.
- Metals (ലോഹങ്ങൾ): shiny, malleable, ductile, good conductors. Non-metals (അലോഹങ്ങൾ): mostly dull, brittle when solid, poor conductors. Metalloids (ഉപലോഹങ്ങൾ): in between.
- Non-metals are at the top right of the periodic table (plus hydrogen at the top left); metalloids (B, Si, Ge, As, Sb, Te) lie along the staircase.
- H 1 · C 2,4 · N 2,5 · O 2,6 · Cl 2,8,7. Families: carbon family, nitrogen family, oxygen family, halogens (ഹാലൊജനുകൾ).
- Non-metals share electron pairs: H–H, Cl–Cl (single), O=O (double), N≡N (triple). H₂, N₂, O₂, Cl₂ are diatomic.
- Allotropes: different forms of the same element with different physical properties (diamond, graphite, fullerene; O₂ and O₃).
- “Hydrogen is in group 1, so it is an alkali metal” ✗ – it is a non-metal gas.
- “Non-metals never conduct electricity” ✗ – graphite does.
- “Allotropes are isotopes” ✗ – isotopes are atoms with different numbers of neutrons; allotropes are different arrangements of the same atoms.
- Writing chlorine as 2,7 ✗ – it has 17 electrons: 2,8,7.