Chemistry The Central Science Notes PDF

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Chemistry: The Central Science Notes Atomic & Molecular Perspective of Chemistry -

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Chemistry: study of the properties and behaviour of matter Matter: physical material of the universe; anything with mass and occupies space Property: characteristic that allow to recognise particular type of matter & to distinguish it from others All matter comprised of combination of about 100 substances called elements Atoms: small building blocks of matter o Each element composed of unique kind of atom o Composition: kinds of atoms the matter contains o Structure: arrangement of atoms Molecules: 2 or > atoms joined in particular shapes 2 realms: o Macroscopic: ordinary-sized objects o Submicroscopic: atoms and molecules

Classifications of Matter -

Typically characterised by: 1. Physical state (gas, liquid or solid) 2. Composition (element, compound or mixture)

States of Matter - Gas (vapour) o No fixed volume/shape, rather it uniformly fills its container o Can be compressed/expanded to occupy smaller/larger volume o Molecules are far apart & moving at high speeds, colliding repeatedly with 1 another & with walls of container o Compressing gas es frequency of collisions between molecules buy does not alter size/shape of molecule. - Liquid o Has distinct volume independent of its container o Assumes shape of the portion of the container it occupies o Not compressible to any appreciable extent o Molecules are packed closely together but still move rapidly o Rapid movement allows molecules to slide over 1 another; thus liquid pours easily - Solid o Both definite shape & volume o Not compressible to any appreciable extent o Molecules are held tightly together, usually in definite arrangements in which molecules can wiggle only slightly in fixed positions o Distances between molecules similar in liquid states

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Changes in temp &/or pressure can lead to conversion of one state to another (e.g. ice melting, water vapor condensing) Pure Substances - Usually referred to simply as a substance - Matter that has distinct properties & a composition that does not vary from sample to sample - E.g. water, table salt - All substances are either: o Elements: cannot be decomposed into simpler substances. On molecular level, each element is composed of only 1 kind of atom o Compounds: composed of 2 or more elements & kinds of atoms. E.g. water (hydrogen & oxygen)

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Mixtures: combinations of 2 or more substances in which each substance retains its chemical identity

Elements - Currently 118 are known (vary in abundance) - Relative abundances of elements:

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Some common elements & their symbols:

Compounds - Formed from interaction with other elements - E.g. when hydrogen gas burns in oxygen gas, the elements H and O combine to form the compound water. Conversely, water can be decomposed into its elements by passing an electrical current through it - Pure water: 11% H & 89% O o Constant ratio; every water molecule has same no. of H & O atoms o 2 H atoms & only 1 O atom per molecule o H atoms are lighter than O atoms Mixtures - Each substance in a mixture retain its chem identity & properties - In contrast to pure substance (fixed composition), the composition of a mixture can vary - Components: substances that make up a mixture - Heterogeneous: mixtures without same composition, properties & appearance throughout (e.g. rock & wood vary in texture & appearance) - Homogenous: mixtures that are uniform throughout (e.g. air is mixture of nitrogen, oxygen & smaller amounts of other gases) o Also called solutions (can be solids, liquids or gases)

Atomic Numbers, Mass Numbers & Isotopes - Atomic number: no. of protons (=electrons) in an atom of any element

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Mass number: number of protons + neutrons in the atom

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All atoms of a given element have same atomic number Isotopes: atoms with identical atomic no. (protons) but different mass numbers (neutrons)

The Periodic Table - Arrangement of elements in order of >ing atomic no. with elements having similar properties placed in vertical columns

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Periods: horizontal rows Groups: vertical columns Metallic elements/metals: all elements on left & in middle except hydrogen o Properties: luster & high electrical & heat conductivity o All except mercury (Hg) are solid at room temperature Non-metallic elements/non-metals: from boron (B) to astatine (At) o Some are solid, gaseous and 1 is liquid at room temp & pressure o Generally diff from metals in appearance & other physical properties Metalloids: along line that separates metals from non-metals

Molecules & Chemical Formulas - Chemical formula: e.g. O2 (subscript shows 2 oxygen atoms present in each molecule) - Diatomic molecule: molecule made up of 2 atoms e.g. H2, N2, O2, Cl2 - Molecular compounds: compounds that are composed of molecules containing more than 1 type of atom e.g. CH4 Molecular & Empirical Formulas - Molecular formulas: chemical formulas that indicate actual no. of atoms in a molecule e.g. H2O2, C2H4 - Empirical formulas: chemical formulas that give only relative no. of atoms of each type in a molecule e.g. HO, CH2 Picturing Molecules - Structural formula: show how atoms are joined together

Ions & Ionic Compounds - Ion: charged particle (electrons removed/added to atom) - Cation: +ve charge - Anion: -ve charge - Polyatomic ions: consist of atoms joined as in a molecule, but carry net +ve or -ve charge e.g. NH4+, SO42- Ionic compounds: compound made up of cations and anions

o Naming:

Alkanes - Compounds containing only carbon & hydrogen called hydrocarbons - Alkanes, simplest class of hydrocarbons, each carbon is bonded to 4 other atoms

Chemical Equations - Used to represent chemical equations - E.g. 2H2 + O2  2H2O - Reactants: left of the arrow - Products: right of the arrow - Number in front of the formulas are called coefficients (indicate relative no. of molecules of each kind involved in reaction) - Needs to be balanced as atoms are nether created or destroyed in any reaction Balancing Equations

Indicating states: - Gas (g) - Liquid (l) - Solid (s) - Dissolved in aqueous (water) solution (aq) Avogadro’s No. & The Mole -

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Mole: counting units for no. of atoms, ions or molecules in a laboratory-sized sample o 1 mole = amount of matter that contains as many objects as the no. of atoms in exactly 12g of isotopically pure 12C Avogadro’s number: no. of atoms in 1 mole of ANY ELEMENT is 6.022 x 1023 o A mole of atoms, molecules or anything else all contain this no. of objects: E.g.

o How large is this number? Pennies placed side by side in straight line would encircle Earth 300 trillion (3 x 1014) times o Mole of any substance contains Avogardro’s cumber Molar Mass - A mole is always the same number (6.02 x 1023), but 1-mol samples of diff substances have diff masses - The atomic weight of an element in atomic mass units is numerically equal to the mass in grams of 1 mol of that element. E.g. ( means therefore)

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The mass of 1 mole, often abbreviated as 1 mol, of a substance (mass in grams per mole) is called molar mass of the substance o Is numerically = to its formula weight in atomic mass units for any substance

Quantitative Info from Balance Equations - The coefficients in a balanced chem equation indicate both the relative number of molecules/formula units in the reaction & the relative number of moles

Limiting Reactants

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When 1 reactant is used up before other, the reaction stops as soon as any reactant id totally consumed, leaving the excess reactants as leftovers. Example: Mixture of 10 mole H2 & 7 mol O2 which react to form water:

o Because 2 mole H2 = 1 mole O2, the no. of moles of O2 needed to react with all the H2 is:

o Because 7 mole O2 is available at the start of the reaction, 7 mol O2 – 5 mol O2 = 2 mole O2 is still present when all H2 is consumed o The reactant completely consumed in a reaction is called limiting reactant (determines, or limits the amount of product formed) o The mole ratio H2:O2:H2O = 10:5:10 = 2:1:2. Theoretical & Percent Yields - Theoretical yield: quantity of product calculated to form when all of a limiting reactant is consumed - Actual yield: amount of product actually obtained (ALWAYS LESS THAN) the theoretical yield - Reasons for diff: o Some reactants may not react (may react in way diff from desired/side reactions) o Not always possible to recover all the product from reaction mixture - Percentage yield:...