All chemicals have what you can call a first and last name. The first name is the cation (positive ion) while the last name is the anion (negative ion). Cations are written as the element name while anions are the element name ending with the suffix “ide.”  The chemical symbol for each element can be found on the periodic table. Unlike covalent compounds, Greek prefixes are not used to indicate the number of atoms of each element. You have to balance the charges of the elements to determine the atoms. For example: Lithium oxide is Li2O. Sometimes the cation or anion is a polyatomic ion. These are molecules that have two or more atoms with ionic groups. There’s no good trick to remembering these, you just need to memorize them.  There are only 3 cation polyatomic ions and they are ammonium (NH4+), hydronium (H3+), and mercury(I) (Hg22+). They all have a +1 charge (though, technically, 2 mercury atoms are bonded together, which creates a 2+ charge, with each mercury cation containing a 1+ charge).  The rest of the polyatomic ions have negative charges ranging from -1 to -4. Some common ones are carbonate (CO32-), sulfate (SO42-), nitrate (NO3-), and chromate (CrO42-). The valence charge can be determined by looking at the position of the element on the periodic table. There are a few rules to keep in mind that help you identify the charges:  All group 1 elements at +1. All group 2 elements are +2. Transition elements will have Roman numerals in parentheses to indicate their charge. Silver is 1+, zinc is 2+, and aluminum is 3+. Group 17 elements are 1-. Group 16 elements are 2-. Group 15 elements are 3-. Remember, when working with polyatomic ions, use the charge of the complete polyatomic ion, rather than the individual ions. Once you have identified the charge of each element (or polyatomic ion), you will use these charges to determine the number of atoms present of each element. You want the charge of the compound to equal zero so you will add atoms to balance the charges. For example: Lithium Oxide. Lithium is a group 1 element and has a +1 charge. Oxygen is a group 16 element and has a 2- charge. In order to balance the 2- charge of the oxygen, you need 2 atoms of lithium; therefore, the chemical formula of lithium oxide is Li2O. The best way to learn formula writing is to practice with lots of examples. Use examples in your chemistry book or look for practice sets online. Do as many as you can until you feel comfortable writing chemical formulas.  Calcium Nitride: Symbol for calcium is Ca and symbol of nitrogen is N. Ca is a group 2 element and has a charge of +2. Nitrogen is a group 15 element and has a charge of 3-. To balance this, you need 3 atoms of calcium (6+) and 2 atoms of nitrogen (6-): Ca3N2. Mercury(II) Phosphate: Symbol for Mercury is Hg and phosphate is the polyatomic ion PO4. Mercury has a 2+ charge as indicated by the Roman numeral II next to it. Phosphate has a 3- charge. In order to balance them, you will need 3 atoms of mercury (6+) and 2 molecules of phosphate (6-): Hg3(PO4)2.
++++++++++
One-sentence summary -- Identify the chemical symbols for the cations and anions. Recognize polyatomic ions. Determine the valence charge of each element. Balance the positive and negative charges of the ions. Practice with some examples.

Article: Take your strand of hair and lift it up a little. Remove the strip covering the adhesive on the bottom extension. Press on the bottom extension underneath the thin strand of hair you're lifting. Take the top extension. After removing the adhesive tape covering that extension, press on top of your strand of hair. The top and bottom extension should stick together. Then press them together with pliers for a few seconds to secure them. If the extensions are not sticking, you used too much hair in your strand. Gently brush some hair off the bottom extension. Move across your side part, repeating this process until you have added all the extensions. The precise number of extensions you are adding depends on the size of your head. You will likely use about 5 rows of hair extensions or more, depending on how voluminous you want your hairstyle to be.  If you plan to add extensions on the sides of your head, leave 1 inch (2.5 cm) of hair out horizontally, closest to the ear, and then continue applying the extensions. If you have a thin hairline, leave about 1 inch (2.5 cm) of hair out across your entire hairline before adding extensions, just to make sure that your hair has enough density to cover the tape-ins without making them noticeable.
Question: What is a summary of what this article is about?
Attach the bottom extension under the thin portion of hair. Secure the top extension. Repeat the process.