Science: Atomic Structure and Electron Configuration
Understanding atoms, subatomic particles, and how electrons are arranged
Science: Atomic Structure and Electron Configuration
Understanding atoms, subatomic particles, and how electrons are arranged
Chemistry - Grade 9-12
- 1
An atom of carbon has an atomic number of 6 and a mass number of 12. How many protons, neutrons, and electrons does a neutral carbon atom have?
Use atomic number for protons and subtract to find neutrons.
A neutral carbon atom has 6 protons, 6 neutrons, and 6 electrons. The atomic number gives the number of protons, the mass number minus the atomic number gives the neutrons, and a neutral atom has the same number of electrons as protons. - 2
An atom has 17 protons and 18 electrons. Identify the element and state whether the particle is a neutral atom or an ion.
The element is chlorine because chlorine has 17 protons. It is an ion, not a neutral atom, because it has one more electron than protons. - 3
Write the full electron configuration for a neutral oxygen atom.
Oxygen has 8 electrons total.
The full electron configuration for neutral oxygen is 1s2 2s2 2p4. Oxygen has 8 electrons, and they fill the lower-energy orbitals first. - 4
Write the noble gas electron configuration for sodium.
The noble gas electron configuration for sodium is [Ne] 3s1. Sodium has 11 electrons, so after the neon core, one electron goes into the 3s orbital. - 5
How many valence electrons does a neutral sulfur atom have? Explain how you know from its electron configuration.
Valence electrons are in the highest occupied energy level.
A neutral sulfur atom has 6 valence electrons. Its electron configuration is 1s2 2s2 2p6 3s2 3p4, and the outer energy level is n = 3, which contains 3s2 and 3p4 for a total of 6 electrons. - 6
Write the full electron configuration for magnesium, which has 12 electrons.
The full electron configuration for magnesium is 1s2 2s2 2p6 3s2. The 12 electrons fill the orbitals in order from lowest energy to highest energy. - 7
A neutral atom has the electron configuration 1s2 2s2 2p6 3s2 3p5. Identify the element and state how many valence electrons it has.
Add the electrons to identify the element, then count the outer-shell electrons.
The element is chlorine. It has 7 valence electrons because the highest occupied energy level is n = 3, and 3s2 3p5 contains 7 electrons. - 8
Compare the relative charges and locations of protons, neutrons, and electrons in an atom.
Protons have a positive charge and are located in the nucleus. Neutrons have no charge and are also located in the nucleus. Electrons have a negative charge and are found in the electron cloud outside the nucleus. - 9
An aluminum atom has 13 protons and a mass number of 27. Find the number of neutrons. Then write the full electron configuration of a neutral aluminum atom.
Subtract protons from mass number to find neutrons.
Aluminum has 14 neutrons because 27 minus 13 equals 14. The full electron configuration of neutral aluminum is 1s2 2s2 2p6 3s2 3p1. - 10
Write the electron configuration for the fluoride ion, F-. Explain how it differs from the electron configuration of neutral fluorine.
The electron configuration for F- is 1s2 2s2 2p6. Neutral fluorine is 1s2 2s2 2p5, so the fluoride ion has gained one extra electron, filling the 2p sublevel. - 11
Why are atoms electrically neutral when the number of protons equals the number of electrons?
Think about how positive and negative charges combine.
Atoms are electrically neutral in this case because protons have a positive charge and electrons have an equal negative charge. When the numbers are the same, the charges balance and the total charge is zero. - 12
A calcium atom is neutral and has 20 electrons. Write its noble gas electron configuration and state how many electrons are in its outermost energy level.
The noble gas electron configuration for calcium is [Ar] 4s2. There are 2 electrons in its outermost energy level because the highest occupied level is n = 4, which contains the 4s2 electrons.