Ordering Principle
Atomic number order: In the modern periodic table, the elements are arranged in a sequence that increases by atomic number. The atomic number is the number of protons found in the nucleus of each atom. As you go from one element to the next, the number of protons increases by one. This order helps keep elements with similar properties in the same columns.
Moseley’s contribution: The idea of arranging elements by atomic number was introduced by a scientist named Henry Moseley. Before him, elements were arranged by atomic weight, but Moseley discovered that atomic number was a better way because it showed repeating patterns of properties more clearly.
Columns and Groups
Vertical groups: If you look at the periodic table from top to bottom, you’ll see vertical columns. These are called groups, and there are 18 of them. Each group contains elements that behave in similar ways in chemical reactions.
Shared properties: Elements in the same group (vertical column) have similar chemical properties. This means they react with other substances in similar ways because they have the same number of outer electrons.
Valence electrons: The reason elements in the same group act similarly is because they have the same number of valence electrons. These are the electrons in the outermost shell of an atom and are involved in chemical reactions.
Group 1 – Alkali metals: The elements in Group 1 are known as alkali metals. These metals are very reactive, especially with water, and include elements like lithium (Li), sodium (Na), and potassium (K).
Group 17 – Halogens: The elements in Group 17 are called halogens. These are very reactive nonmetals, and they include fluorine (F), chlorine (Cl), and iodine (I).
Group 18 – Noble gases: Group 18 contains the noble gases, also called inert gases. These elements, like helium (He), neon (Ne), and argon (Ar), are very stable and don’t usually react with other elements because their outer shells are full.
Rows and Periods
Horizontal periods: The horizontal rows in the periodic table are called periods. There are 7 periods in total, and each one represents a new electron shell being filled.
Electron shells: All the elements in a period have the same number of electron shells. For example, all elements in Period 3 have three shells.
Period 3 range: The third period on the periodic table starts with sodium (Na) and ends with argon (Ar). These elements all have three electron shells but different numbers of electrons in the outer shell.
Valence Electrons
Chemical properties: The way an element reacts with other substances depends on the number of valence electrons it has. These electrons play a major role in forming bonds with other atoms.
Stable configurations: Atoms are always trying to become more stable. Most atoms want to have a full outer electron shell. This means having either two electrons (duplet) for very small atoms or eight electrons (octet) for most atoms. When their outer shell is full, atoms are less likely to react.
General Structure
Element types: The periodic table helps us group elements into three main types: metals (which are shiny and good at conducting electricity), nonmetals (which are often gases or brittle solids), and metalloids (which have properties of both metals and nonmetals).
Transition elements: These are special metals found in the center of the table, between Group 2 and Group 13. They are called transition elements and include elements like iron (Fe), copper (Cu), and zinc (Zn).
Periodic trends: If you look down a group or across a period, you will notice patterns. For example, elements might get larger in size or more reactive. These repeating patterns are called periodic trends.