Electrons, Atomic Number, and Mass Number

This page delves deeper into the arrangement of electrons and introduces the concepts of atomic number and mass number, which are essential for understanding atomic number and mass number in elements gcse.

Definition: Atoms are electrically neutral, meaning the number of electrons equals the number of protons.

The atomic number, also known as the proton number, is introduced as a fundamental property of elements.

Definition: The atomic number is the number of protons in an atom and is unique for each element.

An example is provided using aluminum, which has an atomic number of 13, meaning it has 13 protons and 13 electrons. Its electronic configuration is given as 2,8,3.

Highlight: On the periodic table, atomic numbers increase in order.

The concept of mass number is then explained:

Definition: The mass number is the total number of protons and neutrons in an atom's nucleus.

The page demonstrates how to calculate the number of neutrons by subtracting the atomic number from the mass number.

Example: For Cobalt (Co), with a mass number of 59 and an atomic number of 27, the number of neutrons is 59 - 27 = 32.

The page concludes with exercises on finding atomic numbers, mass numbers, and calculating the number of neutrons for various elements using the periodic table. This information is crucial for students studying detailed explanation of electron configuration in atoms class 9 and higher levels.

The Arrangement of Electrons in an Atom

This page focuses on the arrangement of electrons in atoms, which is essential for understanding chemical bonding and reactivity. This knowledge forms the basis for detailed explanation of electron configuration in atoms pdf.

Definition: Electrons are arranged around the nucleus in energy levels or shells, with the lowest energy level closest to the nucleus.

The page explains that electrons are attracted to the positively charged nucleus and fill the lower energy levels first. It provides a visual representation of the first three energy levels, showing their electron capacities:

1. First level: 2 electrons
2. Second level: 8 electrons
3. Third level: 8 electrons (can hold up to 18)

Example: Lithium, with 3 electrons, has 2 in the first shell and 1 in the outer shell.

The concept of electronic configuration is introduced, using a notation system that represents the number of electrons in each shell.

Example: Chlorine, with an atomic number of 17, has an electronic configuration of 2,8,7.

Highlight: The number of electrons in the outermost shell determines the element's group in the periodic table.

The page concludes with a note on drawing electron shell diagrams, advising students to arrange electrons in pairs and evenly around the circle to avoid losing count.

This information is crucial for understanding the electronic configuration of first 20 elements and beyond, providing a foundation for more advanced topics in chemistry such as chemical bonding and periodic trends.