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Chapter 2

BIL 150 Chapter Notes - Chapter 2: Atomic Nucleus, Atomic Number, Covalent Bond


Department
Biology
Course Code
BIL 150
Professor
Gaines Michael
Chapter
2

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Chapter 2 – The Chemical Context of Life
Organisms are composed of matter, which is anything that takes up
space and has mass
Elements and compounds
oElement – a substance that cannot be broken down to other
substances by chemical reactions (Na)
oCompound – a substance consisting of two or more different
elements combined in a fixed ratio (H2O)
The Elements of Life
oOf the 92 natural elements, about 20-25% are essential elements,
meaning that an organism needs them to live a healthy life and
reproduce (humans need 25 elements, plants need 17)
o96% of living matter is made up of oxygen, carbon, hydrogen, and
nitrogen
oTrace elements are required by an organism in only minute
quantities
Fe (iron) is needed by all forms of life
Atom – the smallest unit of matter that still retains the properties of an
element
oSubatomic particles – neutrons, protons, electrons
oProtons and neutrons are packed together tightly in the atomic
nucleus
oProtons and neutrons have masses close to 1 Dalton
Atomic number (# of protons) and mass number (protons + neutrons)
oIsotopes – some atoms that have more neutrons than other atoms
of the same element and therefore have greater mass
Radioactive isotope – one in which the nucleus decays
spontaneously, giving off particles and energy
The Energy Levels of Electrons
oEnergy – the capacity to cause change (by doing work)
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