what is matter? matter is any substance in the universe that has mass and occupies space all matter...
TRANSCRIPT
What is Matter?
• Matter is any substance in the universe that has mass and occupies space
• All matter is composed of extremely small particles called atoms
• Every atom has the same basic structure– Core nucleus of protons and neutrons– Orbiting cloud of electrons
More
Models
of
Ato
ms
Note electron cloud
Note electron cloud
Look at the samples at the front desk
• Element– A substance that cannot be broken down
by ordinary chemical means (one type of atom)
• Does anyone know the chemical symbol for these?
Iron, Oxygen and Hydrogen • Where can we find this information?
1H
1.0079
12C
12.010
What do these numbers stand for?
What kind of information can we get from the periodic table?
Chemical Formulas• The chemical formula of a substance indicates:
– The elements in the molecule– The number of atoms of each element in the
substance• Example: 6H2S04
– 2 atoms of the element hydrogen; 1 atom of the element sulfur; 4 atoms of the element oxygen
• A number in front of substance indicates how many molecules of that substance there are:– There are 6 molecules of H2S04 in the example
Electron shells
Atomic number = number of protons = number of electrons for element
Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.
Electron shells determine how an atom behaves when it encounters other atoms
Electrons
• Each electron shell has a specific # of orbitals
– First orbital holds up to two electrons
Fig. 3.3
Atoms with incomplete electron orbitals are
more reactive
Stability
• Atoms will react to maintain 8 electrons in their valence shell (except the first shell which is full at 2 electrons)
• If valence shell has less than 8 electrons the atom will gain, lose or share electrons to remain STABLE.
Question: Do you feel good when you and your friend share things? How would you feel if your friend gave you something to make you happy?
http://www.coolcakesbylindsay.com/2012_07_01_archive.html
Types of Chemical Bonds
The Major Chemical Bonds of Biomolecules:
– Ionic Bond– Covalent Bond
• Non-Polar• Polar
-Hydrogen bond
Ionic Bond – Sodium chloride
Sodium tends to give up its single electron in its valence shell
Chlorine pick up one electron to completely fill its valence shell
Ionic Bonds
• Formed when electrons are completely transferred from one atom to another
• During bonding, atoms gain or lose electrons
• Now called ions: negatively or positively charged
• What do we know about + and -?
• Examples; NaCl, CaCl2, K2O
Covalent Bond
• Between nonmetallic elements of similar electronegativity
• Formed by sharing electron pairs
• Examples; O2, CO2, C2H6, H2O, SiC
• 2 types:
- Nonpolar and Polar
- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
Electronegativity
Is a chemical property that is a measure of the tendency of an atom to attract a bonding pair of electrons. (Wikipedia and www.chemguide.co.uk)
•Decreases down a group
•Increases with increasing atomic number going across a period
•Which is more electronegative?
S or Fl, C or O, Mg or P
Put your knowledge to work
Why is H2S a gas and H2O a liquid at room temperature?
Write a response based on the chemistry information you have.
Hydrogen Bonds• Attraction between
partially (-) and partially (+) charged atoms
• Examples:• Exist between
adjacent water molecules
• Between polarized regions of same large molecules (protein)
• Between 2 strands of a DNA molecule