chemistry guide

1. Significant Figures

-Significant figures are critical when reporting scientific data because they give the reader an idea of how well you could actually measure/report your data. Before looking at a few examples, let's summarize the rules for significant figures.

A helpful way to check rules 3 and 4 is to write the number in scientific notation. If you can/must get rid of the zeroes, then they are NOT significant.

Examples: How many significant figures are present in the following numbers?

2. An Isotope is when two of the same elements have equal number of protons but different number of neutrons

- An isotope is basically a variant of a particular element

The three naturally-occurring isotopes of hydrogen. The fact that each isotope has one proton makes them all variants of hydrogen: the identity of the isotope is given by the number of neutrons. From left to right, the isotopes are protium (¹H) with zero neutrons, deuterium (²H) with one neutron, and tritium(³H) with two neutrons.

3. Periodic table

Horizontal rows on the periodic table are called periods. Each row is a new electron shell/energy levels or e- cloud. Energy levels are designated 1-7.

Each shell is broken into subshells/orbitals (region of space where e-‘s are found ~95% of the time). Orbitals are designated s, p, d, and   f. Orbitals hold a max of 2 e-‘s. Vertical columns are called groups or families.

4. Radiocative Decay- 

-Each element has a half life, which is the amount of time for half of the element to decay

Radioactive decay has plenty of uses. one example is preserving food because when food is exposed to ionizing radiation these can eliminate growth. higher doses of radiation can sterilize food products. Other uses include energy production, creating weapons, and even cancer treatment.

Half Life Problem – Assume you have a 200 gram sample of Radon. Its half life is 4 days. How much will remain after 24 days. Answer: 24 days is 6 half lives. 200g 100g50g25g12.5g6.25g3.125g 

5. Bonding 

In chemistry there are different types of bonding. A bond is when a force holds two different atoms together. Atoms will lose or gain electrons in order to gain a full set of 8 valence electrons.