Atomic Structure - Atoms

Learning Objectives

• Know the definition of an element.

• Understand that each type of atom is represented by a specific chemical symbol.

• Know the basic structure and layout of the periodic table.

• Understand the basic structural components of an atom.

Foundations of Matter and Elements

• Substances and Atoms:

  • Millions of different substances are catalogued by scientists, including common materials such as wood, metal, plastic, and glass.

  • All substances are composed of tiny particles called atoms.

  • Approximately $100$ different types of atom occur naturally on Earth.

  • These approximately $100$ atomic types combine in a huge variety of ways to form every existing substance.

• Definition of an Element:

  • An element is a substance made up of only one type of atom.

  • An atom is defined as the smallest part of an element that can exist.

  • Because there are only about $100$ different naturally occurring types of atom, there are only about $100$ distinct elements.

• Physical Properties of Elements:

  • Elements display diverse physical and chemical properties.

  • Metallic elements such as silver, chromium, copper, and gold ($Au$) are shiny solids at room temperature.

  • Non-metallic elements such as oxygen ($O$), nitrogen ($N$), argon ($Ar$), and chlorine ($Cl$) are gases at room temperature.

International Chemical Symbols and the Periodic Table

• International Chemical Nomenclature:

  • Element names vary across different spoken languages (for example, the element sulfur is called schwefel in German and azufre in Spanish).

  • To facilitate communication within the global scientific community, internationally standardized chemical symbols are used to represent elements universally.

  • Chemical symbols in the periodic table represent individual atoms (e.g., $O$ represents an atom of oxygen; $Na$ represents an atom of sodium).

• Structure and Layout of the Periodic Table:

  • All known chemical elements are arranged systematically in the periodic table.

  • Groups:

  • The periodic table is arranged in vertical columns called groups.

  • There are eight main groups in the periodic table.

  • Each group contains elements with similar chemical properties.

  • Specific designated groups and regions in the periodic table include:

    • Group 1: The alkali metals

    • Group 2: The alkaline earth metals

    • Central Block: The transition metals

    • Group 7: The halogens

    • Group 0: The noble gases

    • Lanthanides

    • Actinides

• Classification of Elements Across the Periodic Table:

  • Dividing Line (Staircase): A bold black diagonal 'staircase' drawn on the right side of the periodic table serves as the dividing line between metals and non-metals.

  • Metals: Located to the left of the staircase line.

  • Non-metals: Located to the right of the staircase line.

  • Metalloids (Semi-metals):

  • Elements situated directly next to the bold dividing staircase line.

  • Metalloids exhibit a combination of metallic and non-metallic properties.

  • Examples include silicon ($Si$) and germanium ($Ge$) from Group 4.

Compounds and Chemical Bonding

• Definition and Characteristics of Compounds:

  • The vast majority of substances encountered are compounds rather than pure elements.

  • A compound is made up of different types of atom chemically bonded together.

  • Chemical bonds hold the constituent atoms tightly together in compounds.

• Molecules and Chemical Formulas:

  • A molecule is a grouping of two or more atoms bonded together.

  • Water Molecule ($H_2O$):

  • A sample of pure water always contains twice as many hydrogen ($H$) atoms as oxygen ($O$) atoms.

  • Its chemical formula is written as $H_2O$.

  • If no numerical subscript appears after an atom's chemical symbol in a formula, it is read as $1$.

  • The ratio of hydrogen atoms to oxygen atoms ($H : O$) in water is $2 : 1$.

  • Simple vs. Complex Compounds:

  • Some compounds consist of just two types of atom (e.g., water, $H_2O$, or carbon dioxide, $CO_2$).

  • Most compounds consist of more than two different types of atom.

Basic Structure of an Atom

• Every atom consists of a tiny central core called a nucleus.

• Electrons orbit around the central nucleus.

Key Summary Points

• All substances are composed of atoms.

• Elements contain only one type of atom.

• Compounds contain more than one type of atom.

• The periodic table lists all chemical elements across eight main groups, with each group containing elements that exhibit similar chemical properties.

• An atom consists of a tiny nucleus at its center, surrounded by orbiting electrons.

• Synoptic Link: For detailed additional information on the periodic table of elements, refer to Topic C2.1.

Practice Questions and Exercises

• Question 1a:

  • Task: Arrange these elements into a table showing metals and non-metals: phosphorus ($P$), barium ($Ba$), vanadium ($V$), mercury ($Hg$), krypton ($Kr$), potassium ($K$), and uranium ($U$). [2 marks]

• Question 1b:

  • Task: Classify hydrogen ($H$) as a metal or a non-metal and explain why. [1 mark]

• Question 2:

  • Task: Explain why mixing two elements together allows them to be separated relatively easily by physical means, whereas when two elements are chemically combined in a compound, they are usually difficult to separate. [2 marks]

• Question 3:

  • Task: Draw diagrams to explain the difference between an element and a compound. [2 marks]

• Question 4:

  • Task: Describe the basic structure of an atom. [2 marks]

• Question 5:

  • Task: Find out the Latin words from which the symbols of the following metallic elements are derived:

  • a) Sodium, $Na$ [1 mark]

  • b) Gold, $Au$ [1 mark]

  • c) Lead, $Pb$ [1 mark]

  • d) Potassium, $K$ [1 mark]

• Question 6:

  • Task: Explain what information can be deduced from the chemical formula of carbon dioxide, $CO_2$. [2 marks]