Molecules and Solutions Grade 10 ST

Molecule A molecule is a group of two or more chemically bonded atoms Few elements exist naturally… Can you name a few? Gold Helium The atoms of most elements bond with other elements to form molecules.

A diatomic molecule contains only two atoms H2, N2, O2, Br2, HCl, CO A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4 2.5

Elements All elements of the periodic table are neutral Their atomic number is equal to the number of protons and electrons of the element Therefore they have no charge!

Reminder The noble gases are extremely stable Why? The shell containing the valence electrons is complete!

Atomic Bonding Atoms seek to have a similar configuration to that of the noble gases. Elements are said to follow the octet rule Wanting to follow suit of the closest noble gas with eight electrons Exception: Lithium, beryllium and boron which follow helium: following the duet rule

Electron Tendency Lithium Beryllium Boron Carbon Nitrogen Oxygen Group Number IA IIA IIIA IVA VA VIA VIIA VIIIA Example of Element Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Valence Electrons 1 2 3 4 5 6 7 8 (except He) Tendency Lose 1 e- Lose 2 e- Lose 3 e- Gain or Lose 4 e- Gain 3 e- Gain 2 e- Gain 1 e- None Stable

Facts All Alkali metals have one valence electron, therefore they tend to lose the electron Halogens have 7 valence electrons, tendency to gain one electron Hydrogen is Special It can gain or lose, depending on the circumstances

Ions An ion is an atom, or group of atoms, that has a positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion.

Sodium and Chlorine Sodium is neutral Sodium has 1 valence electron Chlorine is neutral Chlorine has 7 valence electrons Na 11 protons 11 electrons Cl 17 protons 17 electrons

Ionic Bonding =Na+ 2,8 2,8, 1 2,8,7 Cl- 2,8,8

Ions Ions are formed when an atom becomes electrically charged by gaining or losing electrons When an ion is formed the number of protons remains unchanged! When an atom gains one or more electrons it forms a negative ion When an atom loses one or more electron it forms a positive ion.

Most Probable form of ion Most Probable Ions Group Number IA IIA IIIA IVA VA VIA VIIA VIIIA Most Probable form of ion E+ E2+ E3+ E4+ or E4- E3- E2- E- None Example Li+ Be2+ B3+ C4+ or C4- N3- O2- F- He

Polyatomic Ions A group of two or more chemically bonded atoms that has become electrically charged by losing or gaining one or more electrons

Refresher... Solute: The minor component in a solution, dissolved in the solvent Solvent: The liquid in which a solute is dissolved to form a solution

Solutions A solution is a homogenous mixture whose component substances cannot be distinguished, even with the aid of a magnifying instrument In a solution, the solute is dispersed uniformly throughout the solvent. Tap water, air and steel are everyday examples of solutions

Aqueous Many substances can be dissolved in water=aqueous solution The polarity of water allows for this http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

Properties: Concentration The concentration of a solution is the amount of solute present in a given quantity of solution. Change Effect on the Concentration Dilution (addition of solvent) Reduced concentration Dissolution (addition of solute) Increased concentration Evaporation (reduction of solvent)

Expressing Concentration g/L - grams of solute per litre of solution %m/V - grams of solute per 100mL of solution %m/m - grams of solute per 100g of solution %V/V – millilitres of solute per 100mL of solution

Formula C is the concentration (in g/L) m is the mass of the solute (in g) V is the volume of the solution (in L)

Concentration in PPM Parts per million – the number of parts of solute in a million parts of solution 1 ppm = 1 g of solute in 1 000 000 g of solution or to 1 mg of solute in 1000g of solution In an aqueous solution 1 ppm  1 mg of solute per litre