# Midterm Study Guide Project

## By Austin Lim

Sheppard Chem 4th period

## Significant Figures

To start off Significant Figures are each of the digits of a number that are used to express it to the required degree of accuracy, starting from the first nonzero digit.

Rules of Significant Numbers

1. The numbers 1-9 are always significant.

2. Zero is significant only under the following conditions

• When the zero is between two significant figures (Ex:102, 3005)
• Zero is also significant if it follows a decimal point after a significant figure. (Ex: 7.0)
• When it follows after a decimal point and a significant figure. (Ex: 4.750)
3. However Zero is not a significant number under the following conditions
• When zero is used as a placeholder preceding a decimal point. (Ex: 0.75)
• Zero is not significant after a decimal, but before a significant figure. (Ex:0.0077)

If more help is needed here is a link to a video that can help : https://www.khanacademy.org/math/arithmetic/decimals/significant_figures_tutorial/v/significant-figures

## Cation and Anions

How do we determine whether an element will become a cation or an anion when it becomes an ion?

First we need to know what they are...

Ion: Formed when a neutral atom gains or loses electron(s).

Cation: Formed when a neutral atom loses an electron(s) and becomes positively charged.

Anion: Formed when a neutral atom gains an electron(s) and becomes negatively charged.

Ions from Metal Elements

Generally metals lose electrons to form cations with a positive charge equal to the group number. This connects with the octet rule because the metals 'revert' to the octet for the previous row in the periodic table.

Ex: Potassium (K) is in group 1 and has one valence electron and forms a K^1+ (plus 1 charged) cation.

Ions from Nonmental Elements

Generally nonmetal atoms gain electrons to form ions with a negative charge. This connects into the octet rule for their row in the periodic table. To get the charge, the charge equals the group number subtracted by 8. (charge = group number - 8)

Ex: Fluorine (F) is in group 17 and has 7 valence electrons . To get the charge you would subtract 8 from 7 which will give you - 1 . So Fluorine forms a F^1- (negative 1 charged) anion.

If more help is needed this video may help: