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BiologyforNonMajors_02.pptx

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Biology I for Non-Majors

Module 2: Chemistry of Life

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Matter

Matter occupies space and has mass

Elements are unique forms of matter

Specific chemical and physical properties

Cannot be broken down into smaller substances by ordinary means

Designated by chemical symbols

Table 1. Approximate Percentage of Elements in Living Organisms (Humans) Compared to the Non-living World

Element	Life (Humans)	Atmosphere	Earth’s Crust
Oxygen (O)	65%	21%	46%
Carbon (C)	18%	trace	trace
Hydrogen (H)	10%	trace	0.1%
Nitrogen (N)	3%	78%	trace

Atoms

Atom= smallest unit of matter that retains all chemical properties of element

Proton- positively charged particle that resides in nucleus (core of atom)

Electron- negatively charged particle that travels around nucleus

Neutron- mass of 1 and no charge

Atomic number- equal to number of protons

Mass number- number of protons plus neutrons

Periodic Table of Elements- chart that contains atomic and mass number

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Periodic Table of Elements

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Arrangement of Electrons

How elements interact depends on how electrons are arranged

Electrons exist at energy levels that form shells around nucleus- closest shell filled up first (2 electrons)

Second and third energy levels hold up to 8 electrons

7 rows on periodic table- number of shells that elements within row have

Isotopes

Different forms of the same element that have the same number of protons but different number of neutrons

Carbon-12 is most common type of carbon- 6 protons, 6 neutrons

Carbon-14 has 6 protons, 8 neutrons

Radioactive isotopes- unstable isotopes that lose protons or energy

Carbon Dating. Authored by: Bill Faulkner/NPS. Located at: https://www.nps.gov/chis/learn/historyculture/pygmymammoth.htm. License: Public Domain: No Known Copyright

Chemical Bonding

Atom is most stable when all of electron positions in outermost shell are filled- atoms will bond with other elements to fill the outermost shell

This leads to the formation of chemical bonds/interactions between elements

Element can donate, accept, or share electrons with other elements to satisfy octet rule (8 electrons)

Different elements do different things depending on how ‘unfilled’ the outermost shell is

Title: Chemical Bonds. Authored by: BrainPOP Educators. Located at: https://educators.brainpop.com/bp-topic/chemical-bonds/. License: CC-BY

Filling the Outermost Shelli

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Ionic Bonds

Cations- positively charged ions formed by losing electrons

Anions- negatively charged ions formed by gaining electrons

Electron transfer- movement of electrons from one element to another

Electrolytes- necessary for nerve impulse conduction, muscle contractions, and water balance

Full of salts

Found in many sports drinks and dietary supplements that provide these lost during sweating

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Covalent Bonds

Covalent bonds- another way octet rule can be satisfied

Stronger and more common than ionic bonds in molecules of living things

Commonly found in carbon-based organic molecules (DNA/proteins)

Strength is one of main reasons living organisms have difficult getting nitrogen

Formation of water molecules provides example of covalent bonding

https://www.youtube.com/watch?v=QqjcCvzWwww

Polar & Non-Polar Covalent Bonds

Nonpolar- form between two atoms of same element or between different elements that share electrons equally

Polar- electrons shared by atoms spend more time closer to one nucleus than the other= slightly positive or negative charge develops

Covalent bonds between hydrogen and oxygen atoms in water are polar covalent bonds

https://www.youtube.com/watch?v=Mo4Vfqt5v2A

Hydrogen Bonds

Provide many of the critical, life-sustaining properties of water and help stabilize structures of proteins and DNA

When polar covalent bonds containing hydrogen form, hydrogen has slightly positive charge because hydrogen is pulled more strongly

Hydrogen will be attracted to negative charges- weak interaction occurs

Occurs between water molecules- weak and easily broken

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https://www.youtube.com/watch?v=iOOvX0jmhJ4

van der Waals Interactions

Weak attractions or interactions between molecules

Occur between polar, covalently bound atoms in different molecules

Some weak attractions caused by temporary partial charges formed when electrons move around nucleus

Title: Johannes Diderik van der Waals. Authored by: Unknown. Located at: https://commons.wikimedia.org/wiki/File:Johannes_Diderik_van_der_Waals.jpg. License: CC-BY

Why Life Depends on Water

Water is polar

Water stabilizes temperature

Water is an excellent solvent

Water is cohesive

Oil Abstract [247/366]. Authored by: Tim Sackton. Located at: https://flic.kr/p/d6Lq33. License: CC BY-SA: Attribution-ShareAlike

https://www.youtube.com/watch?v=HVT3Y3_gHGg

Water is Polar

Hydrogen and oxygen atoms within water molecules form polar bonds

No overall charge, but slight positive charge on each hydrogen atom and slight negative charge on oxygen atom

Each water molecule attracts other water molecules because of positive and negative charges in the different parts of the molecule

Hydrogen bonds are not readily formed with nonpolar substances such as oil and fats – won’t dissolve in water

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Water Stabilizes Temperature

Hydrogen bonds allow it to absorb and release heat energy more slowly than many other substances

Temperature is measure of kinetic energy of molecules- as motion increases, energy is higher and thus temperature is higher

Water moderates temperature changes within organisms and in their environments

As molecular motion decreases and temperatures drop, less energy is present to break hydrogen bonds between water molecules

When water is frozen, ice is less dense than water

Image is a modification of work by Jane Whitney

Water is an Excellent Solvent

Ionic compounds and polar molecules can readily dissolve in water

Referred to as solvent- substance capable of dissolving another substance

Charged particles will form hydrogen bonds with surrounding layer of water molecules

Positively charged sodium ion surrounded by partially negative charges of oxygen

Negatively charged chloride ion is surrounded by partially positive charges of hydrogen atoms

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Water is Cohesive

Water molecules are attracted to each other, keeping molecules together at liquid-air interface

Gives rise to surface tension- capacity of a substance to withstand rupture when placed under tension

Cohesion and surface tension keep water molecules intact and item floating on top

Cohesive forces related to water’s property of adhesion or attraction between water molecules and other molecules

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pH, Acids, and Bases

pH- measure of its acidity or alkalinity

High concentrations of hydrogen ions yield low pH

pH scale ranges from 0-14

Acids- substances that provide hydrogen ions and lower pH

Bases- provide hydroxide ions and higher pH

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Buffers

Most cells in human bodies operate at pH levels of 7.2-7.6

Outside this range cells no longer function properly and proteins break down

Buffers are key to maintaining the limited pH range cells need

Readily absorb excess H+ or OH–

Carbon dioxide is part of a prominent buffer system in the human body

Quick Review

Can you draw a diagram of an atom, according to current scientific understanding?

Please define the term isotope.

Are you able to describe the behavior and location of electrons, and how these factors influence bond formation between atoms?

What is the octet rule and its role in chemical bonds?

What are the characteristics of ionic/covalent bonds and can you identify common ions of both?

Can you model a Hydrogen bond and identify its unique qualities?

Are you able to model a van der Waals interaction and identify its qualities?

Please describe the properties of water that are critical to maintaining life