Atoms, Elements, and the Chemical Basis of Life: Study Notes for General Biology

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Atoms, Elements, and Matter

Origin and Nature of Matter

The universe and all living things are composed of matter, which is anything that takes up space and has mass. The Big Bang is theorized to have created all the matter in the universe.

Matter: Anything that occupies space and has mass.
All visible matter is made of atoms.
Atoms are the fundamental units of matter.
Example: Biological cells, molecules, and all substances are made of atoms.

Structure of Atoms

Atomic Composition and Properties

An atom consists of a central nucleus containing positively charged protons and neutral neutrons, surrounded by a cloud of negatively charged electrons. Most of the atom's volume is empty space.

Protons: Positively charged particles in the nucleus.
Neutrons: Neutral particles in the nucleus.
Electrons: Negatively charged particles in a cloud around the nucleus.
Electrostatic attraction between protons and electrons keeps electrons near the nucleus.
If the nucleus were the size of a keyboard, the electron cloud would be as large as a football field, illustrating the vast empty space in atoms.
Atoms are mostly empty space; if not, objects would be much heavier.

The Periodic Table of Elements

Classification and Properties of Elements

The Periodic Table organizes all known elements by their atomic number, symbol, and atomic mass. Each element is defined by the number of protons in its nucleus.

Element: A substance that cannot be broken down into simpler substances by chemical means.
Each element has a unique atomic number (number of protons).
Atomic symbol: One or two-letter abbreviation for the element.
Atomic mass: Sum of protons and neutrons in the nucleus.
Formula:
Example: Hydrogen (H) has 1 proton, Helium (He) has 2 protons.

Periodic Table Structure

Elements are arranged in rows (periods) and columns (groups) based on their properties.
Elements in the same group have similar chemical properties.

Isotopes

Definition and Examples

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This difference can affect the atomic mass and stability of the atom.

Isotope: Variant of an element with a different number of neutrons.
Example: Carbon-12 and Carbon-13 are both isotopes of carbon.
Carbon-12: 6 protons, 6 neutrons, stable.
Carbon-13: 6 protons, 7 neutrons, stable.
Some isotopes are unstable and undergo radioactive decay, emitting particles and energy.
Formula for nuclear number:

Elements Essential for Life

Major and Trace Elements in the Human Body

Living organisms are primarily composed of a small subset of elements. Four elements—carbon, hydrogen, oxygen, and nitrogen—make up over 96% of the human body’s mass. Other elements are present in smaller amounts and are essential for various biological functions.

Major elements: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N)
Minor elements: Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg)
Trace elements: Boron (B), Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn)

Element	Symbol	Percentage of Body Mass (including water)
Oxygen	O	65.0%
Carbon	C	18.5%
Hydrogen	H	9.5%
Nitrogen	N	3.2%
Phosphorus	P	1.0%
Potassium	K	0.4%
Sulfur	S	0.3%
Sodium	Na	0.2%
Chlorine	Cl	0.2%
Magnesium	Mg	0.1%
Trace elements	Various	<0.01%

Example: Oxygen is the most abundant element in the human body, primarily found in water and organic molecules.

Atomic Structure and Stability

Electron Clouds and Energy Levels

Electrons form a cloud around the nucleus and occupy specific energy levels or shells. The arrangement of electrons determines the chemical properties and reactivity of the atom.

Electrons repel each other and are distributed in shells at characteristic average distances from the nucleus.
Atoms remain stable when their electron shells are filled according to specific rules (e.g., the octet rule).
Example: Helium has two electrons filling its first shell, making it chemically inert.

Additional info: The notes have been expanded to include definitions, examples, and context for atomic structure, isotopes, and the role of elements in biology, as well as a reconstructed table of elements in the human body.