BIOL 2051 Chapter Notes - Chapter 2: Electron Shell, Atomic Nucleus, Atomic Mass

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Chapter 2 Notes
• All organisms are composed of matter
o Anything that contains mass and can occupy space.
• Can exist in the form of solid, liquid, or gas
• Atoms are the smallest functional units of matter
o Cannot be broken down any further after that.
• When two or more atoms are bonded together, a molecule is formed.
• Each specific atom (ex. N, O, Na) are called elements
o Pure substance of only one kind of atom
• The three subatomic particles: protons(+), neutrons(0), electrons(-)
• Protons and neutrons are confined in the atomic nucleus
o Electrons are around atomic nucleus
• Orbitals: Region of space surrounding nucleus with a high probability of have an
electron.
• Electron shells: composed of one or more orbitals
• Energy: Ability to promote change or do work
• Electrons have kinetic energy: energy of moving matter
• Electron shells may contain one or more orbitals, with each orbital containing up to two
electrons.
o First shell (innermost): can only have 2 electrons
o Second shell: four orbitals that can hold up to four pairs of electrons or 9 electrons
all together
• Electrons are found in orbitals of varying shapes (spherical or propeller-type shapes)
• Atoms that have unfilled electron shells tend to share, lose, or gain electrons in order to
fill the shell
o Electrons that are on the outermost shell are called valence electrons
• Atomic number – amount of protons
• Protons and neutrons are nearly equal in mass
• Electron mass is ignored in calculations
• Atomic mass is measured in daltons
• Avogadro’s number (measured in atoms) = 6.022 x 10^23
• Isotopes: an element that exist in many different forms that differ in the number of
neutrons
• For example, the most abundant form of the carbon atom, 12C, contains six protons and
six neutrons, and thus has an atomic number of 6 and an atomic mass of 12 Da. The
superscript placed to the left of 12C is the sum of the protons and neutrons. The rare
carbon isotope 14C, however, contains six protons and eight neutrons.
• Radioisotopes: isotopes found in nature that are inherently unstable.
• Organisms are composed of four elements: oxygen, carbon hydrogen, and nitrogen
o Typically 95% of the organism’s mass
o Hydrogen and Oxygen (in form of water) make up 60% (95% in plants)
• Carbon is a major building block of all living matter
• Nitrogen is the vital element in all proteins
• In addition, all living organisms require trace elements
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