Sec 2- Chemical Foundation Flashcards
Unit I- The Basis for Life
What is matter?
This is anything that occupies space and has mass.
The three states if matter are;
* Gas
* Liquid
* Solid
All matter consist of atoms.
An atom is the fundamental building-block of matter.
What is the structure of atoms?
These are composed of subatomic particles.
- A proton is positively chargeed… # determines element
- An electron is negatively charged… # determines ion
- A neutron is electrically neutral… # determines isotope
What are the regions of an atom?
Protons and neutron are in the center (nucleus). Electrons whiz around the nucleus in shells/orbitals.
What is an element?
A pure substance that consists only of atoms with the same number of protons.
What is the Periodic Table?
An organization of the elements.
- created in 1869 by Dmitri Mendeleev
- elements are organized by increasing number of protons
- 118 elements (94-98 occur naturally)
- element abbreviated by first letter (or two) in English or Latin
- Ex C for carbon and Ca for calcium
What is the atomic number?
This is based on the number of protons in the atomi nucleus.
- Located above the abbreviation of the element.
- Determines the element
- If the atom is neutral, it will also indicate the number of electrons.
What are isotopes?
Different forms of an elements that differ in the number of neutrons their atoms carry.
- Different isotopes have different masses because neutrons are heavy.
- Neutron= 1 amu
- Proton= 1 amu
- Electrons= 0 amu
- amu= atomic mass unit (or dalton)
- One amu= 1.7 x 10^-24 g
- Every form of an element is an isotope
- Only some are radioactive!
What is mass number?
This is the total number of protons and neutrons in the nucleus of an element’s atoms.
- Located underneath the chemial symbol.
- The number of neutrons can be determined by subtracting the atomic number form the mass number.
- The mass number is also sometimes called the atomic mass.
What are radioactive isotopes?
Isotope with an unstable nucleus, such as carbon-14.
What is radioactive decay?
The process by which atoms of a radioisotope spontaneously emit energy and subatomic particles when their nucleus disintegrates.
The half life of carbon-14 is 5,730 yrs, which makes carbon dating possible.
What are electron shells?
Electrons travel around the nucleus in different orbitals (shells; Bohr model).
1st shell can “hold” two electrons
2nd shell can “hold” eight electrons
3rd shell can “hold” eight electrons
What are vacancies?
Atoms are “happiest” when they have no vacancies in their outer shell (valence shell).
This is called the octet rule, because besides the innermost shell, it takes eight electrons to fill a shell.
Atoms with vacancies in their outer shells tend to interact with other atoms.
Atoms get rid of vacancies by gaining or losing electrons, or sharing electrons with other atoms.
What are ions?
The negative charge of an electron balances the positive charge of a proton in the nucleus.
Changing the number of electrons may fill its outer shell, but changes the charge of the atom.
ion- atom that carries a charge because it has an unequal number of protons and electrons.
How is an ion formed?
An atom that gains electrons has a negative and is now called an ion, specificallt an anion.
Ex: Cl^-, F^-, Br^-
The suffix “-ide” is added to anions
Chlorine becomes chloride
How are cations formed?
Atoms can also lose elctrons from their valence shell.
They are then positive ions, or cations.
Their valence shell is now also completely full.
Ex: Na^+, Mg^2+, K^+, Ca^2+
What are chemical bonds?
Forms when the elctrons of two atoms interact.
Holds the two atoms together.
What is the molecule?
Group of two or more atoms joined by chemical (covalent) bonds.
Ex: H2O, C6H12O6, H2
What are compounds?
Type of molecule that has atoms of mroe than one element.
Ex: NaCl, H2O, CH4
H2 and O2 are molecules but NOT compounds.
What are ionic bonds?
A strong mutual attraction formed between ions of opposite charge.
- Ionic bonds are formed between oppositely charged ions.
- Opposites attract
- For ions to form there had to be a loss and gain of electrons.
- Specific gain or loss
What are covalent bonds?
Two atoms sharing a pair of electrons.
- A covalent bond forms when two atoms hsare one or more pairs of outer-shell (valence) electrons.
- Covalent bonds are much tronger than ionic bonds.
- Covalent bonds between aotms form molecules.
- Sharing instead of gaining or losing.
What are polar molecules?
Unequal sharing of electrons makes a polar molecules.
- The electrons of covalent bonds are not always shared equally between the atoms of different elements, like in the example of water.
- Electrons prefer being around the big, positive nucleus of the oxygen atom instead of the small positive nucleus of the hydrogen atoms.
- There is a partial positive charge by the hydrogen atoms and a partial negative charge by the oxygen atom.
- Unequal sharing makes water a polar molecule.
- But remember that overall, H2O is a neutral molecule.
What are Hydrogen Bonds?
The polarity of water results in weak electrical attractions between neighboring water molecules. These interactions are called hydrogen bonds.
- Hydrogen bonds form and break more easily than covalent or ionic bonds - they do not form molecules - they are not chemical bonds.
- However, the vast number of hydrogen bonds make them a powerful entity in biology.
- Hydrogen bonds impart unique properties to substances such as water, and hold molecules such as DNA in their characteristic shapes.
What are Van Der Waals Interactions?
Van Der Waals interactions are weak attractions between molecules or parts of a molecule due to slight fluctuations in electrical densities around the different atoms.
Proteins, for example, have a characteristic 3D shape because of covalent, ionic, hydrogen, and van de Wals forces.
How important is water?
All living organisms are mostly comprised of water (humansd = 60-70%), and all chemical reactions of life are carried out in water.
Hygrogen bonds between water molecules give water unique properties that make life possible.
