Transcript chp 4 formation of compounds power point

Formation of compounds
Salt: a familiar compound
• Sodium Chloride – NaCl (1 sodium with 1
chlorine)
• Uses flavor enhancer, manufacture sodium
and chlorine, melt ice
• Physical properties: White, crystalline cube
shape, brittle,800*C mp, solid non conductor,
liquid conductor as well as aqueous
• Chemical properties: stable (unreactive)
Sodium and Chlorine
• Properties of sodium (Na)- shiny, silvery-white,
soft, metal, 98*C mp, so reactive stored in oil,
not found free
• Properties of Chlorine (Cl2)– Pale green,
poisonous gas, odor, kills living cells, soluble in
water, disinfectant, -34*C bp,
Carbon dioxide
• CO2 formula (1 carbon and 2 oxygen)
• Colorless gas, metabolic by-product, used for
photosynthesis
• Physical properties: odorless, tasteless, -80*C
bp - sublimes into dry ice, soluble in water,
weak conductor (aq), burn C to make
• Chemical properties: stable, some fire
extinguishers – not support burning.
Carbon and oxygen
• Carbon – nonmetal, black, burns, organic
chemistry studies.
• Oxygen – nonmetal, colorless, odorless, gas,
21% air, supports burning (reacts), -183*C bp,
slightly soluble in water (fish gills), 46% of
Earth’s crust
Water
• H2O formula (2 hydrogen and 1 water)
• Occurs in all 3 states of matter, 100*C bp, 0*C
mp, Pure water – non conductor, universal
solvent
• Stable, medium for chemical reactions,
photosynthesis starting material,
Hydrogen and oxygen
• Hydrogen: Lightest, most abundant element in
universe, nonmetal, odorless, colorless, gas,
reactive –seldom free, -253 bp, nonconductor,
slightly soluble
• Oxygen: same as before.
How elements form compounds
• Atoms of the element must collide to react
their electron clouds. The outer, valence
electrons are chiefly responsible for chemical
properties and how they will react.
• Noble gas chemical stability – not a single
compound found naturally, (Xe and Kr
artificially made with F using high
temperature and pressure)
Octet rule
• Each noble gas has a filled valence shell, He
with 2 and the rest with 8. Octet rule state
that atoms can become stable by having 8
electrons in the outer energy level. This is
known as a noble gas configuration.
Electrons can be transferred
• Na (metal) with 1 valence electrons transfers its
electron to Chlorine (nonmetal) with 7 valence
electrons, to form ions (atoms with a charge due
to loss or gain of electrons). Sodium ion is now
like Neon and Chlorine is now like Argon.
• The ion opposite charges attract each other
forming an ionic bond. The shape for NaCl is a
crystal, a regular repeating arrangement of
atoms, ions or molecules.
Ionic compounds properties
• Solid, hard, brittle, crystal, high melting and
boiling points, electrolyte – conducts
electricity when dissolved in water due to the
formation of ions.
• All are macroscopic evidence for the strength
and rigidity of the submicroscopic structure of
the salt crystal.
Electrons can be shared
• Hydrogen (nonmetal) and oxygen (nonmetal)
in water. They collide with enough energy to
react, but not enough to take electron, they
combine by sharing.
• Attraction of 2 atoms by sharing a pair of
electrons is called a covalent bond. Compound
held together this way is a covalent
compound. A molecule is an uncharged group
of 2+ atoms held together by a covalent bond.
Steps for writing electron- dot
structures
• Step 1 Determine the total number of valence
electrons in all atoms
• Step 2 Place singe bonds between set of atoms.
Each single bond uses 2 valence electrons
• Step 3 Subtract the electrons used to bond the
atoms, and arrange the remaining to give each
atom an octet. Hydrogen only need a single
bond.
• Step 4 If octet of all atoms cannot be completed
using the remaining elects, rearrange to for a
double or triple bond. Check for octet for each.
More than 2 electrons can be shared
• When charcoal burns, carbon atoms collide
with oxygen to form CO2. When you put
together, oxygen still need 1 electron each.
They share 2 pairs of electrons, forming a
double covalent bond.
Explaining properties of covalent
compounds
• The forces between particles that make up a
substance are called interparticle forces. The
difference in strength explains the properties.
• Many Covalent compound are liquid or gases
at room temperature (sugar is crystal solid –
low melting point), nonconductor in pure
state.