The Periodic Table’s Shape Explained

When you look at the periodic table, it may look scattered, almost unorganized. You may wonder, why isn’t it simply a rectangle, and what are all those letters and numbers on it? 
The shape of the periodic table is determined by the elements’ atomic number, valence electrons, and the number of energy levels they contain. Reading from left to right, we will notice that the number at the very top of the box, called the atomic number, increases with each following element. The atomic number is also what defines an element because the atomic number is equal to the number of protons in that element. In any element, the number of protons, positive particles in the nucleus of elements, is what makes it that specific element. Therefore, if we have an element with three protons, we know it is lithium because the number of protons equals the atomic number of the element.
The valence electrons and chemical properties of an element determine its column on the periodic table. Valence electrons are the electrons on the outermost energy level of an atom. All atoms have energy levels, starting from the innermost that holds two electrons, the next level with eight, and each following level having a specified capacity for electrons. Therefore, on the leftmost column of the periodic table, all those elements have only one valence electron, meaning their outermost energy level only has one electron. However, in the rightmost column, all the elements have the maximum valence electrons for the element. However, this gets more complex when we go lower in the periodic table, so another way to recognize groups, or columns, is by their similar chemical properties. Since the elements in the same column have the same number of valence electrons, they have similar reactivity among other chemical characteristics.
The number of energy levels of an element determines which row, or period, it belongs to. In the first period, we have hydrogen and helium, both of which only have one energy level, therefore placing them in the very first row. However, in the next period, all the elements require two energy levels to hold all their electrons. From this , we know that if we were to take the element magnesium (atomic number 12), that it would have three energy levels since it’s in the third period!
Now let’s do a little trivia! Find calcium (Ca).

1. What is the atomic number? 
   
2. Which group does it belong to?
   
3. Which period does it belong to?
   
4. How many protons does it have?
   

Answers: 1. 20; 2. 2; 3. 4; 4. 20 (in order)