PS.4 The student will investigate and understand the organization and use of the periodic table of elements to obtain information. Key concepts include
1. symbols, atomic number, atomic mass, chemical families (groups), and periods
2. classification of elements as metals, metalloids, and nonmetals
3. formation of compounds through ionic and covalent bonding

Elements

• There are more than 110 known elements.
  • No element with an atomic number greater than 92 is found naturally in measurable quantities on Earth.
  • The remaining elements are artificially produced in a laboratory setting.
  • Elements combine in many ways to produce compounds that make up all other substances on Earth.

Periodic Table

• The periodic table of elements is a tool used to organize information about the elements.
  • Each box in the periodic table contains information about the structure of an element.
  • An atom’s identity is directly related to the number of protons in its nucleus.
  • This is the basis for the arrangement of atoms on the periodic table of elements.


• The vertical columns in the table are called groups or families.
  • Elements in the same column (family) of the periodic table contain the same number of electrons in their outer energy levels.
  • This gives rise to their similar properties and is the basis of periodicity — the repetitive pattern of properties such as boiling point across periods on the table.
• The horizontal rows are called periods.
  • The periodic table of elements is an arrangement of elements according to atomic number and properties.
  • The information can be used to predict chemical reactivity.
  • The boxes for all of the elements are arranged in increasing order of atomic number.

Metals and Nonmetals

• The elements have an increasing nonmetallic character as one reads from left to right across the table.
• Along the stair-step line are the metalloids, which have properties of both metals and nonmetals.
• The nonmetals are located to the right of the stair-step line on the periodic table.
• Metals tend to lose electrons in chemical reactions, forming positive ions.
• Nonmetals tend to gain electrons in chemical reactions, forming negative ions.
  

Reactions and Chemical Bonding

• Gaining or losing electrons makes an atom an ion.
• Gaining or losing neutrons makes an atom an isotope.
• However, gaining or losing a proton makes an atom into a completely different element.

• Atoms react to form chemically stable substances that are held together by chemical bonds and are represented by chemical formulas.
• To become chemically stable, atoms gain, lose, or share electrons.
• Compounds are formed when elements react chemically.
• When a metallic element reacts with a nonmetallic element, their atoms gain and lose electrons respectively, forming ionic bonds.
• Generally, when two nonmetals react, atoms share electrons, forming covalent (molecular) bonds.