Midterm Study Guide Project
Significant Figures and Cation/Anion
By Austin Lim
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)
- 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:https://www.youtube.com/watch?v=mHkrPT_NFCQ
"Significant Figures." Khan Academy. N.p., n.d. Web. 06 Jan. 2016.
"Prediction of Ionic Charges." Prediction of Ionic Charges. N.p., n.d. Web. 06 Jan. 2016.