First, read the English article below.

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... 

Now, please write a short abstract for it in Vietnamese. Abstract:
Xác định ký hiệu hóa học của cation và anion. Nhận biết các ion đa nguyên tử. Xác định điện hóa trị của mỗi nguyên tố. Cân bằng điện tích âm và dương của các ion. Thực hành với vài ví dụ.