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”
H2O: subscript indicates 2 hydrogen
atoms and 1 oxygen atom (water)
CO2: 1 carbon with 2 Oxygen (carbon
dioxide)
C3H8: 3 carbon with 8 hydrogen(propane)
C6H12O6: 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)
Compound
Na2SO4
Al2O3
CaSO4
C2H6
Fe
NH3
Symbol and #
of atoms
Na=2,S=1,O=4
Total # of
atoms
7
(small note sheet)
• The SAME elements can
be used to form VERY
DIFFERENT
compounds with
DIFFERENT properties.
(small note sheet
•
•
•
•
•
•
WATER vs HYDROGEN
PEROXIDE
H2O
2:1
Clear
Colorless
Odorless
Needed for Survival
•
•
•
•
•
•
•
•
•
H2O2
2:2
Clear
Colorless
Odorless
Thick, Syrupy
Kills Bacteria
Poisonous if ingested
Can be used as fuel
• NITROGEN & OXYGEN
NO ( 1N , 1O)
• Nitrogen Monoxide: By product of
combustion of substances in air,
engine, fossil fuels, power plants,
lightning
• Nitrous Dioxide: Brown toxic gas,
NO2 ( 1N , 2O)
major air pollutant, used in racing
N2O ( 2N, 1O)
• Nitrous Oxide: Used by dentist,
surgery as mild anesthetic,
greenhouse gas
• (just COOL INFO!!)
N2O ~ 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 1st
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.
2.
3.
All matter is composed
of atoms
Atoms of a given
element are identical
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
• 6CO2 + 6H2O + Energy
C6H12O6 + 6O2
• CELLULAR RESPIRATION = reverse of
photosynthesis, the production of Carbon Dioxide, Water &
Energy from combustion of glucose, using Oxygen
• EXOTHERMIC
• C6H12O6 + 6O2
6CO2 + 6H2O + Energy
Exothermic & Endothermic Reactions…
work together to CREATE SYSTEMS OR CYCLES!!
• PHOTOSYNTHESIS = making glucose (sugar) & Oxygen
from Carbon Dioxide,Water & Energy
• ENDOTHERMIC
• 6CO2 + 6H2O + Energy
C6H12O6 + 6O2
• CELLULAR RESPIRATION = reverse of
photosynthesis, the production of Carbon Dioxide, Water &
Energy from combustion of glucose, using Oxygen
• EXOTHERMIC
• C6H12O6 + 6O2
6CO2 + 6H2O + 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