How do you find core and valence electrons?

To find core and valence electrons in an atom, you need to understand the electron configuration of that atom. Electron configuration describes how electrons are distributed in the various energy levels or electron shells around the nucleus of an atom. Core electrons are those found in the innermost electron shells, while valence electrons are found in the outermost electron shell. Here's how you can determine them:

Determine the Atomic Number:
Start by identifying the atomic number (Z) of the element you're interested in. The atomic number tells you the number of protons in the nucleus, which is also equal to the number of electrons in a neutral atom.

Write the Electron Configuration:
You can write the electron configuration of an element using a notation that indicates how many electrons are in each energy level or electron shell. There are several methods to write electron configurations, but one common way is using the Aufbau principle, the Pauli exclusion principle, and Hund's rule. The periodic table can also be a helpful reference for electron configurations.

For example, let's consider the element oxygen (O) with an atomic number of 8:

The first energy level (n=1) can hold up to 2 electrons.
The second energy level (n=2) can hold up to 8 electrons.
The electron configuration of oxygen is written as: 1s² 2s² 2p⁴.

Identify Core and Valence Electrons:

Core Electrons: These are the electrons in the inner electron shells (lower energy levels) of the atom. In the example of oxygen, the innermost shell is the 1s², so the 1s² electrons are core electrons.
Valence Electrons: These are the electrons in the outermost electron shell (highest energy level). In the example of oxygen, the outermost shell is the 2nd shell, and the electrons in 2s² and 2p⁴ collectively form the valence electrons. So, in this case, there are 6 valence electrons.
So, in summary, to find core and valence electrons:

Determine the atomic number.
Write the electron configuration.
Identify the electrons in the innermost shell as core electrons and those in the outermost shell as valence electrons.
Understanding the distribution of core and valence electrons is important in chemistry because it helps predict an element's chemical properties and its ability to form chemical bonds with other elements. Valence electrons, in particular, play a crucial role in chemical reactions and bonding.