Elements and Elements and CompoundsCompounds

Elements Elements

Element—simplest form of matter with Element—simplest form of matter with unique set of properties.unique set of properties.

Cannot be broken down into more simple Cannot be broken down into more simple unitsunits

Example: Hydrogen, Oxygen, Carbon Example: Hydrogen, Oxygen, Carbon symbolized by letters in the periodic tablesymbolized by letters in the periodic table

H, O, CH, O, C

CompoundsCompounds

Mixed molecules made of two or more Mixed molecules made of two or more elements chemically combined in a elements chemically combined in a fixed fixed proportion.proportion.

Compounds can be broken down into Compounds can be broken down into simpler substances (elements) using simpler substances (elements) using chemical Rx.chemical Rx.

Example Water: H2O can be broken down Example Water: H2O can be broken down into Hydrogen and Oxygen gas into Hydrogen and Oxygen gas (electrolysis)(electrolysis)

Breaking CompoundsBreaking Compounds

physical methods (cutting, filtration, physical methods (cutting, filtration, distillation) do nott workdistillation) do nott work

To break down compounds, To break down compounds, chemical chemical change is needed.change is needed.

Example: burning or oxidization reactionsExample: burning or oxidization reactions

Breaking CompoundsBreaking Compounds

Properties of compounds are different than Properties of compounds are different than those of their component elements.those of their component elements.

Example Example

Compound NaCl (table salt): white crystalsCompound NaCl (table salt): white crystals

Na: sodium…soft metalNa: sodium…soft metal

Cl: chlorine…green poisonous gasCl: chlorine…green poisonous gas

Breaking CompoundsBreaking Compounds

Electricity can be used to break down the Electricity can be used to break down the compound water into hydrogen and compound water into hydrogen and oxygen. oxygen.

Oxidization can be used to break sugar Oxidization can be used to break sugar (C6H12O6) into Carbon and H2O, CO2(C6H12O6) into Carbon and H2O, CO2

Distinguishing Substances and Distinguishing Substances and MixturesMixtures

Substance:Substance:Composition cannot by changed by physical Composition cannot by changed by physical

means only by chemical means, means only by chemical means, compounds/elementscompounds/elements

Mixture:Mixture:Composition of a material can be changed easily Composition of a material can be changed easily

(filtration, destillation….) can homogeneous or (filtration, destillation….) can homogeneous or heterogeneousheterogeneous

Homogeneous mixtures cannot be easily Homogeneous mixtures cannot be easily distinguished from substances!!!!distinguished from substances!!!!

Element Symbols Element Symbols

Chemists use chemical symbols to represent Chemists use chemical symbols to represent elements elements

First letter of a chemical symbol is always First letter of a chemical symbol is always capitalized.capitalized.

If 2If 2ndnd letter is used, it is lowercase letter is used, it is lowercase C-CarbonC-Carbon Na-SodiumNa-Sodium Fe-IronFe-Iron Many symbols are from the language in which Many symbols are from the language in which

the element was first identified.the element was first identified.

FormulasFormulas

Chemists use chemical formulas to Chemists use chemical formulas to represent compoundsrepresent compounds

Subscripts in chem. formulas indicate the Subscripts in chem. formulas indicate the relative proportion of elements in a relative proportion of elements in a compoundcompound

CC66HH1212OO6 6 is glucoseis glucose6 Carbons, 12 Hydrogens, 6 Oxygens6 Carbons, 12 Hydrogens, 6 Oxygens