Question

name: teacher: date: q1 chemistry: u2l10 periodic table practice
prepwork part 2: electron configuration
directions: read the passage below. as you read, annotate the important information and vocabulary words. then answer the questions.
**part 1: read & annotate:
atoms are made up of protons, neutrons, and electrons. electrons are found in regions around the nucleus called electron shells or energy levels. electron configuration is a way to show how these electrons are arranged around the nucleus in an atom
each energy level can hold a certain number of electrons:

• 1st level: up to 2 electrons
• 2nd level: up to 8 electrons
• 3rd level: up to 18 electrons
• 4th level: up to 32 electrons

within each energy level, each orbital holds a certain number of electrons

• s orbital holds a maximum of 2 electrons
• p orbital holds a maximum of 6 electrons
• d orbital holds a maximum of 10 electrons
• f orbital holds a maximum of 14 electrons

electrons fill the lowest energy levels first before moving to higher ones. this is called the aufbau principle.
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d...
how to write a full electron configuration (step - by - step)
to write the full electron configuration for a neutral atom, follow these steps:

1. determine the number of electrons - this is the same as the atomic number for a neutral atom.
2. use the aufbau principle - fill orbitals in order of increasing energy. the typical order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d...
3. fill each orbital with the correct number of electrons - s orbitals hold 2 electrons, p holds 6, d holds 10, and f holds 14.
4. stop when youve used up all the electrons - check your total to match the number of electrons in the atom.

example: write the full electron configuration of carbon (atomic number = number of protons = 6):

• carbon has 6 electrons.
• fill orbitals in this order: 1s² 2s² 2p²
• so, the electron configuration is: 1s² 2s² 2p²

note: when you add the exponents, it should equal the number of electrons you calculated. 2 + 2+2 = 6 (neutral carbon has 6 electrons)
more examples
sodium (atomic number 11)
configuration: 1s² 2s² 2p⁶ 3s¹
aluminum (atomic number 13)
configuration: 1s² 2s² 2p⁶ 3s² 3p¹
part 2: questions based on reading and examples

1. write the full electron configuration for beryllium (atomic number 4).
2. which element has the configuration 1s² 2s² 2p⁶ 3s²?

Explanation:

Step1: Determine number of electrons for Beryllium

A neutral Beryllium atom has 4 electrons as its atomic number is 4.

Step2: Fill orbitals using Aufbau Principle

Start with 1s orbital which holds 2 electrons, then move to 2s orbital which holds 2 electrons. The electron - configuration is $1s^{2}2s^{2}$.

Step3: Determine element for given configuration

For the configuration $1s^{2}2s^{2}2p^{6}3s^{2}$, sum the electrons. $2 + 2+6 + 2=12$. The atomic number of an element is equal to the number of electrons in a neutral atom. The element with atomic number 12 is Magnesium.

Answer:

1. $1s^{2}2s^{2}$
2. Magnesium