BIOL 111 Chapter Notes - Chapter 2: Endorphins, Atomic Nucleus, Unified Atomic Mass Unit

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4 Feb 2017
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The Chemical Context of Life
Thursday, January 26, 2017
8:18 PM
"Matter consists of chemical elements in pure form and in
combinations called Compounds"
What is matter?
Matter is anything that takes up space and has mass
Organisms are composed of matter
Matter exists in many forms; rocks, metals, oils, gasses, and living organisms
Mass vs. Weight
Mass: Amount of matter in an object
Weight: How strongly mass is pulled by gravity
Elements and Compounds
Element: A substance that can not be broken down to other substances by chemical reactions
Scientists have recognized 92 elements that occur in nature (gold, copper, carbon, etc.)
Of the 92 elements 20-25% are essential elements (elements an organism needs to live a healthy life and reproduce)
Each element consists of a certain type of atom that is different from the atoms of any other elements.
Compound: A substance containing two or more elements combined in a fixed ratio.
Sodium chloride (NaCl) is a combination of the elements Sodium and chlorine in a 1:1 ratio
Atom: Smallest unit of matter that still retains the properties of an element
Composed of subatomic particles
Subatomic Particles
Neutrons: Electrically neutral
Protons: One unit of positive charge
Electrons: One unit of negative charge
Directly involved in chemical reactions
Atomic nucleus: Dense core where protons and neutrons are packed together. Electrons form a cloud around nucleus.
The attraction keeps electrons in the vicinity of the nucleus
For atoms and subatomic particles we use a unit of measure called the dalton (John Dalton; british scientist
who helped develop atomic theory around 1800)
Neutrons and Protons have masses close to 1 dalton
Atomic Number and Atomic Mass
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Atomic Number: Number of protons in an element
All atoms of a particular element have the same number of protons in their nuclei
Written as a subscript to the left of symbol for the element
Mass Number: Total number of protons and neutrons in the nucleus of an atom
Mass number= number of protons + number of neutrons (12)
Atomic number= number of protons= number of electrons in a neutral atom (6)
Number of neutrons: mass number - atomic number (6)
Atomic Mass: Total mass of an atom
Isotopes
Isotopes: Different atomic forms of the same element that have more neutrons than other atoms, and therefore
have a larger mass
Radioactive isotopes: Isotope where the nucleus decays spontaneously, giving off particles and energy
Radiometric Dating:
Radioative Decay can be used to date relics of past life, and provide a large body of evidence for evolution
Half life: "parent" isotope decays into "daughter" isotope at this fixed rate, the time it takes for 50%
of the parent isotope to decay
Half life is not effected by temperature, pressure etc.
Radiometric Dating: Scientists measure the ratio of different isotopes and calculate
how many half lives in years have passed since the organism was fossilized
Energy levels of Electrons:
An atoms electrons vary in the amount of energy they possess
Energy: The capacity to cause change/ do work
Potential Energy: Energy that matter possesses because of it's location or structure
An electron's energy level is correlated with it's average distance from the nucleus, they are found in
different electron shells, each with an energy level
The first shell is closest to the nucleus, and have the lowest potential energy
Electrons in the second shell have more energy, and even more in the third shell
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