Elements to Compounds NCSCOS 4.02

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

*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 (small note sheet)

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)

Molecules (small note sheet) Def: A group of atoms held together by a covalent bond. EX: Water Molecules: Compounds Atoms: Elements *(note sheet) Chemical formulas= use chemical symbols and subscripts to show how many atoms of those elements are combined in the compound (RATIO!)

Chemical Formulas (small note sheet) 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 (water) CO 2 : 1 carbon with 2 Oxygen (carbon dioxide) C 3 H 8 : 3 carbon with 8 hydrogen(propane) C 6 H 12 O 6 : 6 carbon, 12 hydrogen, and 6 oxygen (glucose)

Fill in the Chart (pls place in ntbk) (please just do a practice one in notebook w/notes) 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

(small note sheet) The SAME elements can be used to form VERY DIFFERENT compounds with DIFFERENT properties.

(small note sheet 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

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 (just COOL INFO!!) NO ( 1N, 1O) NO 2 ( 1N, 2O) N 2 O ( 2N, 1O)

N 2 O ~ Nitrous Oxide

2.2D Chemical Bonds (small note sheet) Chemical bonds are forces (the “glue”) that hold atoms together. 2 types: 1.Ionic Bonds: valence electrons completely transferred 2.Covalent bonds: valence electrons shared

IONIC BONDS Attraction between (+) & (-) ions = ionic bonds Ionic compounds are very stable & their strong crystal structure, shatters, separates into ions when dissolved – conduct electricity, high Boiling Point & Melting point 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-)

PROPERTIES OF IONIC BONDS (small note sheet) 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

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

PROPERTIES OF COVALENT BONDS COVALENT BONDS…… *electrons shared between nonmetal and nonmetal *not hard (think of a plastic ball pit)…softer *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

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

3.3D-Chemical Reactions Involve ENERGY Changes Bond energy = energy associated with bonds between atoms Breaking bonds uses (requires) energy Forming bonds gives off (releases) energy

IF…… More energy is RELEASED than added EXOTHERMIC REACTION Reactants YIELD PRODUCTS + ENERGY (baggy of Yeast + Hydrogen Peroxide) More energy is ABSORBED than released ENDOTHERMIC REACTION Reactants + Energy YIELD PRODUCTS (baggy of Baking Soda + Vinegar)

Exothermic & Endothermic Reactions… work together to CREATE SYSTEMS OR CYCLES!! PHOTOSYNTHESIS = making glucose (sugar) & Oxygen from Carbon Dioxide,Water & Energy ENDOTHERMIC 6CO 2 + 6H 2 O + Energy C 6 H 12 O 6 + 6O 2 CELLULAR RESPIRATION = reverse of photosynthesis, the production of Carbon Dioxide, Water & Energy from combustion of glucose, using Oxygen EXOTHERMIC C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy

Exothermic & Endothermic Reactions… work together to CREATE SYSTEMS OR CYCLES!! PHOTOSYNTHESIS = making glucose (sugar) & Oxygen from Carbon Dioxide,Water & Energy ENDOTHERMIC 6CO 2 + 6H 2 O + Energy C 6 H 12 O 6 + 6O 2 CELLULAR RESPIRATION = reverse of photosynthesis, the production of Carbon Dioxide, Water & Energy from combustion of glucose, using Oxygen EXOTHERMIC C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy

REVIEW CHEMICAL REACTION HINTS…. 1) Temperature Change …Heat…Energy…Produced = ?

FIRE COMBUSTION EXPLOSION

Your shirt has white spots because you dyed eggs using vinegar?

COLOR CHANGE

BUBBLES ARE PRESENT???

GAS PRODUCED

A SOLID IS FORMED….when u started with LIQUIDS????

PRECIPITATE