Biology Chap 2 Essay

Biology- Chapter 2

Book Notes

2.1 Matter Consists of Chemical Elements in pure form and in combinations called compounds

Elements & Compounds
An element is a substance that cannot be broken down to other substances by chemical reaction
Ex. Na- Sodium
A compound is a substance consisting of 2 or more different elements combined in a fixed ratio
Ex. NaCl- Sodium Chloride
The elements of life
About 20%-25% of the 118 elements are essential elements that an organism needs to have to live a healthy life
O, C, H, N, make up 96% of living matter
Ca, P, S, K, acct for the rest of an organisms mass
Trace elements are required by an organism in minute quantities

2.2 An Elements Properties depend on the structure of its atoms
An atom is the smallest unit of matter that retains the properties of an element
Subatomic Particles
Atoms are composed of even tinier bits of matter called subatomic particles
Neutrons (neutral)
Protons (+)
Electrons (-)
Protons and Neutrons are packed together in the atomic nucleus
Positive charge
The rapidly moving electrons form a “cloud” around the nucleus
The opposite forms of attraction keep the atoms circulating the nucleus
Dalton- the measurement of subatomic particles (amu)
Atomic # & Atomic Mass
All atoms of a particular element have the same # of protons in their nuclei
Called the atomic number
Written as a subscript to the left of the symbol of the element
Ex. 11Na
Tells you the # of P & E
We can deduce the # of neutrons from the mass #
Mass= the sum of P& N
Na= Mass of 23 & atomic # of 11
Subtract the Mass (23) from the # (11)= 12 Neutrons
The mass #is an approx. of the total mass
Isotopes
All atoms of a given element have the same number of protons but can differ in the number of neutrons, giving them a greater mass—These different forms of the same element are called Isotopes
Stable Isotopes- Their nuclei do not have a tendency to lose subatomic particles, a process called Decay
A radioactive isotope is one in which the nucleus decays spontaneously, giving off particles and energy.
Radioactive Tracers
Radioactive tracers are also used in combination with sophisticated imaging instruments, such as PET scans that can monitor growth and metabolism of cancers in the body.
Radiation from decaying isotopes also poses a harm to life by damaging cellular molecules
Radiometric Dating
A parent isoptope decays into its “daughter” isotope at a fixed rate, expressed as the Half Life of the isotope
Radiometric Dating, scientists measure the ratio of different isotopes and calculate how many half lives have passed since an organism was fossilized or a rock was formed
The energy level of Electrons
Only electrons are directly involved in chemical reactions
Energy is defined as the capacity to cause change
Potential Energy- the energy that matter possess because of its location or structure.
The electrons of an atom have potential energy due to their distance from the nucleus. The negatively charged electrons are attracted to the positively charged nucleus.
So, the more distant the electron is from the nucleus, the greater the potential energy in that electron
An electron can only exist at certain energy levels, never between them
Electron’s energy level is correlated with it’s average distance from the nucleus. Electrons are found in different electron shells, each with a characteristic average distance and energy level
The first shell is closet to the nucleus so these electrons have a lower potential energy
An electron can only move from one shell to another by absorbing or losing an electron
When an electron absorbs energy, it moves to a shell father out from the nucleus
When an electron loses energy, it moves to a shell closer to the nucleus
The lost energy during this process is usually released in the air as heat
The elements are arranged in 3 rows or periods, corresponding to the # of electron shells
The chemical behavior of an elements mainly depends on the # of electrons in its outermost

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