1 / 16

USEFUL DEFINITIONS

USEFUL DEFINITIONS. Element A substance which cannot be split into anything simpler by chemical means. Atom The smallest part of an element that can take part in a chemical reaction. Molecule The smallest particle of a compound (a combination of two or more elements).

thi
Download Presentation

USEFUL DEFINITIONS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. USEFUL DEFINITIONS Element A substance which cannot be split into anything simpler by chemical means. Atom The smallest part of an element that can take part in a chemical reaction. Molecule The smallest particle of a compound (a combination of two or more elements). It is also the name given to the smallest part of those elements which do not exist as atoms in the free state i.e. hydrogen H2 oxygen O2 nitrogen N2 fluorine F2 chlorine Cl2 bromine Br2 iodine I2 N.B. ionic compounds (e.g. sodium chloride) do not exist as molecules.

  2. USEFUL DEFINITIONS Ion The name given to any electrically charged atom or molecule. • positively charged ions are known as cations • negatively charged ions are known as anions Like charges repel but unlike (opposite) charges attract. If the sum of all the positive charges is equal and opposite to all the negative charges then the species will be neutral (no overall charge). Symbol A symbol represents one atom, or one mole, of an element.

  3. Valency Is a numerical measure of the combining power of an atom / ion. Historically, it was the number of hydrogen atoms which will combine with one atom, or group of atoms. It is also the number of positive (+) or negative (-) charges on an ion. e.g. Mg+2, K+,S2-

  4. Valency may also be defined as the number of electrons that an atom donates or accepts to form the duplet state (i.e., 2 electrons in outermost shell) or octet state (i.e., 8 electrons in outermost shell). The valency of an element is always a whole number.

  5. TABLE OF VALENCY

  6. Valencies of some elements & Radicals

  7. Elements With Variable Valencies

  8. USEFUL DEFINITION Formula A formula represents one molecule of a compound, or the simplest ratio of the ions present. As with symbols, a formula represents a single particle or one mole of particles. The number of atoms or groups of atoms in a formula is given by putting a small number just below and behind the symbol(s). As the appearance of a symbol indicates one atom is present, a 1 isn’t written (you put NaBr not Na1Br1). In some formulae brackets are used to avoid ambiguity. Aluminium sulphate has the formula Al2(SO4)3 to show that there are two Al’s to every three SO4‘s. Without the brackets it would appear as though there were forty three O’s i.e. Al2SO43.

  9. Using valency to write chemical formulaeThe following steps are to be considered when writing chemical formulae • Write each symbol • Write the valency at the top right-hand side of each symbol • Cross over the valencies • Write the crossed-over valency at the bottom right of the other symbol. • Where necessary simplify the ratio of valencies

  10. Example what is the formula of aluminium oxide?Answer .1. Al O2. Al3O23. Al2O34. Al2O3Hence, the chemical formula of aluminium oxide is Al2O3

  11. Chemical formula of Calcium hydroxide1. Ca OH2. Ca2 OH13. Ca1 OH24. Ca(OH)2Hence, the chemical formula of calcium hydroxide is Ca(OH)2 ,

  12. chemical formula of Magnesium oxide1. Mg O2. Mg2 O23. Mg2 O2 4. Mg2 O25. MgOHence, the formula of Magnesium oxide is MgO

  13. Iron (III) Sulphate1. Fe SO42. Fe3SO423. Fe2SO434.Fe2(SO4) 3The chemical formula of Iron (III) Sulphate is Fe2(SO4) 3

  14. CONSTRUCTION OF FORMULAE It is useful to learn some formulae... Acids hydrochloric acid HCl nitric acid HNO3 sulphuric acid H2SO4 ethanoic acid CH3COOH Gases ammonia NH3 carbon dioxide CO2 carbon monoxide CO methane CH4 sulphur dioxide SO2

  15. Write the formulae for the following compoundssodium sulphatezinc carbonatecopper I nitratePotassium chloridesulphuric acidIron II nitrateLead II carbonateCalcium hydroxideMagnesium sulphate

  16. Practical word equation1. calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide + water2. copper + silver nitrate = copper nitrate + silver3. methane + oxygen = carbon dioxide + water4. sulphuric acid + magnesium = magnesium sulphate + hydrogen5. copper (II) carbonate = copper (II) oxide + carbon dioxide6. iron (II) sulphate + sodium hydroxide = iron (II) hydroxide + sodium sulphate

More Related