2. Elements to Compounds NCSCOS 4.02

3. Big Picture Elements are pure substances with only ONE type of atom. Most matter is a combination of elements Atoms  elements  molecules  compounds Vocab terms: compound, molecule, chemical formula, subscript, ionic bond, covalent bond

4. 2.1D – ELEMENTS combine to form Compounds 1) 2 or more DIFFERENT elements 2) Held together by CHEMICAL BONDS 3) The type of ATOM & the BOND determine the properties

5. Compounds….. Important characteristics of COMPOUNDS: 1.have a definite composition 2.can be broken down into simpler substances by chemical means 3.can be identified by their physical properties 4.Compounds usually have very different properties than the elements that compose them EX: Ca (soft, silvery metallic solid; needed by humans); Cl (greenish-yellow gas; poisonous to humans) BUT..CaCl (nonpoisonous white solid used to melt ice on streets)

6. Molecules Def: A group of atoms held together by a covalent bond. Molecules: Compounds Atoms: Elements Compounds and molecules are often expressed as chemical formulas: Chemical formulas= use chemical symbols and subscripts to show how many atoms of those elements are combined in the compound (RATIO!)

7. Chemical Formulas Formulas are written with chemical symbols and subscripts which indicate the # of times that element appears in the molecule. Elements without a subscript have an imaginary “1” H 2 O: subscript indicates 2 hydrogen atoms and 1 oxygen atom CO 2 : 1 carbon with 2 hydrogen C 3 H 8 : 3 carbon with 8 hydrogen C 6 H 12 O 6 : 6 carbon, 12 hydrogen, and 6 oxygen

8. Fill in the Chart (pls place in ntbk) CompoundSymbol and # of atoms Total # of atoms Na 2 SO 4 Na=2,S=1,O=47 Al 2 O 3 CaSo 4 C2H6C2H6 Fe NH 3

9. SAME ELEMENTS…. DIFFERENT COMPOUNDS The SAME elements can be used to form VERY DIFFERENT compounds with DIFFERENT properties.

10. WATER vs HYDROGEN PEROXIDE H 2 O 2:1 Clear Colorless Odorless Needed for Survival H 2 O 2 2:2 Clear Colorless Odorless Thick, Syrupy Kills Bacteria Poisonous if ingested Can be used as fuel

11. NITROGEN & OXYGEN Nitrogen Monoxide: By product of combustion of substances in air, engine, fossil fuels, power plants, lightning Nitrous Dioxide: Brown toxic gas, major air pollutant, used in racing Nitrous Oxide: Used by dentist, surgery as mild anesthetic, greenhouse gas NO ( 1N, 1O) NO 2 ( 1N, 2O) N 2 O ( 2N, 1O)

12. N 2 O ~ Nitrous Oxide

13. Chemical Bonds Chemical bonds are forces (the “glue”) that hold atoms together. 2 types: 1.Ionic Bonds: valence electrons transferred 2.Covalent bonds: valence electrons shared

14. IONIC BONDS Attraction between (+) & (-) ions = ionic bonds Ionic compounds are very stable & their crystals are very strong Naming ionic compounds – Positive Ion always named 1 st Negative Ion is named by dropping last part of name & adding the suffix “ide ” EX: Sodium Chloride (Na+Cl-)

15. PROPERTIES OF IONIC BONDS IONIC BONDS…. * occur when metals react with nonmetals * hard (think of a LEGO structure) *brittle *high melting & boiling points *transfer of electrons *conduct electricity when dissolved in water EX: salt, concrete, sulfuric acid

16. COVALENT BONDS Electrons are SHARED… neither atom “loses or gains”…SO…NO IONS are formed! SHARED ELECTRONS are attracted to both positively charged nuclei EX: H2, N2, O2….. The # of covalent bonds an atom can form depends on the # of electrons available for sharing POLAR COVALENT: when electrons are shared unequally (polar-anything that has 2 extremes) EX: H2O

17. PROPERTIES OF COVALENT BONDS COVALENT BONDS…… *electrons shared between nonmetallic elements *not hard (think of a plastic ball pit) *not brittle *low melting & boiling points *don’t conduct electricity well & usually don’t dissolve in water; are usually more flammable EX: O2, CO2, methane, hydrochloric acid, candy corn

18. Atomic Theory Proposed in 1808 by John Dalton. 1.All matter is composed of atoms 2.Atoms of a given element are identical 3.Atoms of different elements combine in simple, whole- number ratios to form chemical compounds