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The Periodic Table
Different atoms have different numbers of protons and electrons--causing all the differences in physical properties of matter.
Elements: Different types of atoms are called elements. They are made of unique atoms.
Periodic Table: Elements are presented in a chart called the periodic table, which lists and organizes every element in boxes. Each element is assigned a chemical symbol which is one or two letters. The first letter is uppercase while the second letter (if there is a second letter) is lowercase. For example, oxygen is represented as O, while zinc is represented as Zn.
How do you make sense of the periodic table?
Each square in the periodic table has information about the element. The top number is its atomic number and the bottom one is its atomic mass.
Atomic number: The atomic number is the number of protons an atom contains. Elements are differentiated by their atomic numbers because each element has a different number of protons.
Atomic mass: Atomic mass is the average mass of a typical atom of that element.
The periodic table is organized by row and column. Each horizontal row is called a period, while each vertical column is called a group or family. The elements are arranged in order of their atomic numbers--so as you go across, each element has one more electron and has one more proton. Hydrogen has 1, helium has 2, and so on. Elements in the same group (column) share similar chemical and physical properties.
Period: A row of elements across the periodic table.
Group or family: A column of elements in the periodic table. Groups of elements have similar physical and chemical properties.
Why atoms form compounds
Atoms alway want to be in a stable state. Many atoms find stability by combining with other atoms. That means giving away, taking, or even sharing electrons with other atoms.
When electrons from different atoms pair up, they form a chemical bond. This chemical bond is the force that holds atoms together. Only electrons in the outer rings--valence electrons--form bonds.
How to write a chemical formula
Chemical formula: Every compound contains a specific ratio of elements. A chemical formula is sort of like the compound’s recipe--it describes the ingredients and their quantities. In a chemical formula, each element is written using its chemical symbol, which is a one- or two-letter symbol, with a subscript beneath the symbol defining the number of atoms.
Sugar contains 12 carbon, 22 hydrogen, and 11 oxygen atoms. So the chemical formula is C12H22O11.
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