The Chemistry of LifeBiology – Unit 3

Put the following words in order from smallest to largest:◦ Cell, atom, organelle, subatomic particle,

molecule, tissues, organism, organ, macromolecule, organ system

The Complexity of Life

Basic unit of matter Atoms are EXTREMELY small

◦ If placed side by side, 100 million atoms would make a row only 1 cm long!

◦ http://learn.genetics.utah.edu/content/begin/cells/scale/

Atoms are made up of…

Atoms

The three subatomic particles: ◦ Protons◦ Neutrons ◦ Electrons

Subatomic particles

Protons and neutrons have about the same mass.

Protons and neutrons are located in the nucleus of an atom

Protons:◦ Positively charged particles (p+)

Neutrons:◦ Particles that carry no charge◦ “neutral” (no)

Protons and Neutrons

Negatively charged particles (e-) Much smaller than the mass of a proton In constant motion in the space surrounding

the nucleus Atoms have equal numbers of electrons and

protons (negative and positive charges balance out) and atoms are neutral

Electrons

Where have you heard of the term “elements” before in science? Can you think of any examples?

Element: pure substance that consists entirely of one type of atom

Periodic Table of Elements

Elements

Periodic Table of Elements

How many protons does a sodium (Na) atom have?

How many neutrons does a flourine (F) atom have?

What is the atomic mass for oxygen (O)? What is the atomic number for phosphorus

(P)?

Practice Problems

Representing Atoms

Atomic model for Carbon◦ Record how many protons, electrons and neutrons

are present in a carbon atom using periodic table◦ Draw the atomic model for carbon◦ Practice with atomic models and beads

Practice

Using your notes and a periodic table, work with a partner to model then sketch each atom in your lab notebook.

For each atom record:◦ Name of element AND symbol◦ # electrons◦ # protons◦ # neutrons

Build and draw the following atoms:◦ C, H, N, P, O, S

Modeling Atoms Lab

Look at the outer orbital of each atom that you made a model of. How do you think the number of electrons on the outer energy level (valence shell) relates to how stable the element is?

Answer: ◦ Elements with full outer orbitals (valence shells)

are more stable and less reactive◦ Elements with partially complete valence shells

are more reactive

Questions

Based on what you know about certain elements and their Bohr model, find an element that would have a full valence shell (stable)

Questions

Fill in each statement

◦ A change in the number of protons =

◦ A change in the number of neutrons =

Questions

Atoms of an element that have different numbers of neutrons.

Total number of protons and neutrons is the mass number (#protons + # neutrons = mass number)

Isotopes

Isotope # protons # electrons # neutrons

Carbon – 12Nonradioactive

6 6 6

Carbon – 13Nonradioactive

6 6 7

Carbon – 14Radioactive

6 6 8

Radioactive elements have unstable nuclei ◦ When nuclei are unstable they break down at

constant rate over time Used in determining age of rocks and fossils Used to detect and treat cancer Used as a “tracer” to follow movement of

substances within organisms.

Radioactive Isotopes

Chemical compound-◦ Substance formed by the chemical combination of

two or more elements in definite proportions.◦ Written in chemical formulas

Examples:◦ H2O: 2 hydrogens : 1 oxygen◦ NaCl 1 sodium : 1 chlorine◦ NaOH 1 sodium : 1 oxygen : 1 hydrogen◦ CO2 1 carbon : 2 oxygens

Chemical Compounds

H20 vs. H2O2

When the ratio of elements in a compound changes, the physical and chemical

properties change as well.

Chemical Compounds

Atoms are held together by chemical bonds 2 main types:

◦ Ionic bonds◦ Covalent bonds

Chemical Bonding

Model and draw a sodium (Na) and a chlorine (Cl) atom

How many valence electrons are in the outer shells of each atom?

Which atom could easily lose an electron? Explain

Which atom could easily gain an electron? Explain

Lab Activity

Formed when one or more electrons are transferred from one atom to another

Atoms lose or gain electrons◦ Lose electrons becomes positively charged

(+)◦ Gain electrons becomes negatively charged

(-) Atoms that have gained or have lost

electrons are ions

Ionic Bonds

Ionic Bonds

Model and draw the ionic bond between the sodium and chlorine ions, then draw below.

Lab Activity Continued

Methane, CH4, is a molecule that is made up of one carbon atom and four hydrogen atoms.

What do you notice about the outer shell (valence shell) of each of these atoms?

Lab Activity Continued

Electrons are shared between atoms The structure that is formed when two or

more atoms are joined by covalent bonds is a molecule

Covalent Bonds

In order to form the CH4 molecule, the atoms covalently bond to each other. Draw the CH4 molecule on your paper.

Lab Activity Continued

How do the valence electrons influence molecular bonding?

Answer:◦ Number of open placed on the valence shell

determines the number of bonds the atom can make

Questions

Carbon dioxide, CO2, is a molecule that is made up of one carbon atom and two oxygen atoms.

What do you notice about the outer shell (valence shell) of each of these atoms?

Lab Activity Continued

In order to form the CO2 molecule, the atoms covalently bond to each other. Draw the CO2 molecule on your paper.

Lab Activity Continued