Biology Chapter 2

Atomic reactions

attain stability by sharing or losing or gaining electrons. In either case, atoms are bonded together into stable associations (MOLECULES)

Electronegativity

attractive force an atomic nucleus exerts on electrons in a covalent bond. depends on how many positive charges it has (nuclei w/more protons are more positive and more attractive to electrons) AND distances between electrons in the one and nucleus (closer electrons, greater the electronegative pull) Hydrogen & oxygen bonds to form water- Es tend to be nearer oxygen because it is more electronegative.

Atomic weight

average of the mass numbers of a representative sample of atoms of that element, with all isotopes in naturally occurring proportions ie, carbon = 12.011 ("fractional atomic weight")

Compound

substance made up of molecules w/2 + elements bonded together in a fixed ratio. each has a molecular weight = sum of atomic weights of all atoms in molecule ***check how to calculate, pg 26

Octet rule & examples

tendency of atoms to form stable molecules so that they have 8 Es in outermost shell ex: Carbon & Nitrogen. Exception- hydrogen, attains when 2 Es occupy its single shell

Mass

measure of the quantity of matter present. Mass of a proton serves as a standard unit of measure--dalton or atomic mass unit (amu) single proton or neutron has a mass of 1 dalton (da)= 1.7 x 10^-24 grams. electron weighs less, effectively zero (9 x 10^-28).

Electrons contribution to the atom

negligible mass but determine how atoms will combine with other atoms to form stable associations

Polar covalent bonds

partial charges resulting produce polar molecules or polar regions of large molecules. polar bonds w/in molecules greatly influence interactions they have with other polar molecules. H2O is a polar compound, and polarity has significant effects on its physical properties and chemical reactivity.

Elements & properties

pure substance containing only one kind of atom. Properties that distinguish them from other atoms include mass and how the interact and associate with other atoms

Covalent bond types

same elements covalently bonded= equal sharing of pairs different- not necessarily equal due to one nucleus exerting greater attractive force on the electron pair than the other so pair closer to that atom NONPOLAR COVALENT- If 2 atoms close to each other in electronegativity, they will share electrons equally (for example, two oxygen atoms each with electronegativity of 3.5 will share electrons equally). POLAR COVALENT- electrons drawn to one nucleus more than to the other. (example, oxygen & hydrogen bond ---oxygen has slightly negative charge/delta negative, hydrogen slightly positive charge/delta positive). Polar= opposite charges separated at the two ends of the bond

Bohr model

see pg 22; representation of helium atom

Covalent bond; strength & orientation; notation

two atoms attain stable electron numbers in their outermost shells by sharing one or more pairs of electrons (example: H2--hydrogen) each electron is attracted to the other atom's nucleus, and the nucleus attracts its own electron. the atoms move closer together and share the electron pair in a covalent bond. very strong- takes a lot of energy to break them. at temps in which life exists, covalent bonds of biological molecules are stable, as are their 3D structures. orientation- for given pair, length always the same. for a given atom w/in a molecule, angle wrt other bonds is generally the same*** pg 26 each line or pair of dots represents a pair of electrons. -single bond is sharing of single pair -double bond is sharing of 4 electrons (2 pairs) -triple bond- six shared electrons- rare, in Nitrogen gas (in air we breathe)

Radioisotopes & uses

unstable and spontaneously give off alpha, beta, gamma radiation (energy) from the nucleus. Release of energy (radioactive decay) transforms original atom. Transformation varies, but some can change number of protons, so original atom becomes a different element. Used in molecules as a tag or label. Also used to date fossils. Low doses of radiation can be damaging. Cobalt-16 is see in medicine to kill cancer cells.

How abundant are the elements in the periodic table?

98 % of the mass of living organisms composed of 6 elements: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur

How are covalent bonds formed in methane gas?

CH4 carbon atom has 6 Es {2 inner, 4 unpaired in outer shell} can form up to 4 covalent bonds by sharing reacts with 4 hydrogens to have a stable 8 electron outer shell

Hydrogen isotopes

Hydrogen 1/1 (1P, o N) Deuterium 2/1 (1 P, 1 N) Tritium 3/1 (1 P, 2 N)

Parts of the atom

Nucleus- dense & positively charged Electrons- move around nucleus, negatively charged (-1) Protons- contained in the nucleus, positively charged (+1) Neutrons- no electrical charge, contained in the nucleus (may or may not contain neutrons) Protons=electrons in an atom; atoms are electrically neutral

Isotopes

Number of neutrons differ; different isotopes of same element have same number of protons/different neutrons. Mostly stable.

Atomic notation

Number of protons in the nucleus is the atomic number and differentiates the atom. Atomic number is unique to each element and does not change. Mass number of an atom is total number of neutrons and protons in its nucleus (ALL atoms with exception of hydrogen has one or more neutrons)

How electron position determines effect on atom

S fills first, electrons have lowest energy level Outermost holds 8. In any atom, outermost electron shell (VALENCE SHELL) determines how the atom combines with other atoms/behaves chemically. ex- valence shell with four orbitals contains 8 Es- stable. Atoms with 1 + unpaired electrons in outer shells capable of reacting.

Importance of sodium, potassium, calcium, iodine, magnesim

S/P- essential for nerve function Calcium- can act as biological signal Iodine- component of a vital hormone Magnesium- bound to chlorophyll in plants

Carbon isotopes

carbon-12 (6 neutrons); carbon-13 (7 neutrons); carbon-14 (eight neutrons) {all three have 6 protons}

Electrons functions, locations

determines how it will combine with other atoms/chemical reactions alter atomic compositions of substances and thus alter their properties. rx involve changes in distribution of electrons between atoms location is impossible to determine. region of space where electron is found at least 90 percent of the time is the orbital.

Orbitals/amount of shells

electron shells. characteristic shapes and orientations can have a maximum of 2 electrons. Farther shell from nucleus, higher the energy level is for electron in the shell. **any atom larger than helium (atomic number 2) must have electrons in 2 or more orbitals. First shell- 1 orbital, s orbital. [Hydrogen- 1, helium, 2] Second shell- four orbitals (s orbital and 3 p orbitals) holds up to 8 electrons Additional shells- elements w/10 + electrons have 3 or more electron shells. {s orbitals are sphere shape, p orbitals are at right angles; orientation contributes to 3D shapes of molecules when atoms link to other atoms}

Chemical bond types

force linking two atoms together in a molecule two types- covalent (sharing of electrons) ionic (atom gains or loses one or more electrons to achieve stability)

Examples of stable electrons

helium, neon, argon.