diff --git a/Grade 10/Science/SNC2DZ/Unit 1: Chemistry.md b/Grade 10/Science/SNC2DZ/Unit 1: Chemistry.md
index 1fb20d3..14e24e7 100644
--- a/Grade 10/Science/SNC2DZ/Unit 1: Chemistry.md	
+++ b/Grade 10/Science/SNC2DZ/Unit 1: Chemistry.md	
@@ -3,6 +3,7 @@
 - Matter - has mass, takes up space.
     - fundamental unit -> ATOMS
 - One `formula unit` - repeating strucure in an ionic compound taht has the simplest ratio of ions in the compound
+- Ions are particles with charges
 
 ## Atoms
 - Atoms are the smallest unit of an element that still retains its properties
@@ -55,6 +56,7 @@
 - Most metals are considered to be multi-metals
     - can form ions of differing charges 
     - add roman numerals to the ions name to indicate its charge, for example, iron($`III`$) oxide.
+
 ## Non-Metals
 - They are dull, bad conductors - insulators
 - Tend to gain electrons
@@ -93,3 +95,21 @@
 |$`K_3P`$|Potassium phosphide|
 |$`Mg_3P_2`$|Magnesium phosphide|
 
+## Polyatomic Ions
+- Ions that are made of $`\ge 2`$ atoms.
+- Molecules with a charge
+- eg. $`CaCo_3`$
+    - $`Ca \rightarrow`$ Calcium ion $`Ca^{2+}`$ `(Cation)`
+    - $`CO_3 \rightarrow`$ Carbonate ion $`CO_3^{2-}`$ `(Anion)`
+    - Calcium carbonate
+- The ones that are not multi-valent are:
+    - The first 20 elements
+    - alkali metals
+    - alkaline earth metals
+    - non-metals (the ones hugging the staircase are also non-metals (some of the metalloids))
+    - halogens
+    - noble gases
+
+- Going down diagonally from aluminium, we get a pattern of 3+, 2+, 1+ of charge. Aluminium has a charge of 3+, Zinc has a charge of 2+, and silver has a charge of 1+, and they
+are all mono-valent. (not multi-valent)
+- If there is more than one polyatomic ion in a formula unit, then surround the ion with brackets