Chemistry — Orbitals & Electron Configuration

What is an orbital?

a region of space around the nucleus where an electron is most likely to be found

How is an orbital usually defined more precisely?

the volume of space where an electron spends about 90% of its time

Why can't we say exactly where an electron is?

electrons have wave-like behaviour, so we can only give probabilities of where they are

How many electrons can a single orbital hold?

two

Why does the orbital model replace simple circular orbits?

electrons do not circle the nucleus like planets, they occupy probability regions of various shapes

What is the difference between a shell and a subshell?

a shell is a main energy level, while a subshell is a set of orbitals of one shape within that shell

What are the four subshell types called?

s, p, d, and f

What is another name for an electron shell?

an energy level

What shape is an s subshell?

a single spherical orbital

What shape is a p subshell?

three dumbbell-shaped orbitals at right angles to each other

How many orbitals does an s subshell have?

one

How many orbitals does a p subshell have?

three

How many orbitals does a d subshell have?

five

How many orbitals does an f subshell have?

seven

How many electrons can an s subshell hold?

two, since it has one orbital

How many electrons can a p subshell hold?

six, since it has three orbitals

How many electrons can a d subshell hold?

ten, since it has five orbitals

How many electrons can an f subshell hold?

fourteen, since it has seven orbitals

How do you work out a subshell's electron capacity?

multiply its number of orbitals by two

Which subshell does the first shell contain?

only the 1s subshell

Which subshells does the second shell contain?

the 2s and 2p subshells

Which subshells does the third shell contain?

the 3s, 3p, and 3d subshells

What is an electron configuration?

a shorthand showing which subshells an atom's electrons occupy

In the notation 2p6, what does each part mean?

2 is the shell, p is the subshell, and 6 is the number of electrons in it

What is the lowest-energy orbital that fills first?

the 1s orbital, closest to the nucleus

What is the order the first few subshells fill in?

1s, then 2s, then 2p, then 3s, then 3p

Why does the third electron in an atom go into the 2s orbital?

the 1s orbital is already full with two electrons, so the next electron moves up a level

Write the electron configuration for an atom with 1 electron?

1s1

Write the electron configuration for an atom with 2 electrons?

1s2

Write the electron configuration for an atom with 3 electrons?

1s2 2s1

Write the electron configuration for an atom with 6 electrons?

1s2 2s2 2p2

Write the electron configuration for an atom with 10 electrons?

1s2 2s2 2p6

An atom has atomic number 18. How many electrons does a neutral atom have?

18, equal to its number of protons

What is the Aufbau principle?

electrons fill the lowest-energy subshells first before moving to higher ones

What does Aufbau mean, and why is it a fitting name?

it is German for building-up, since electrons build up from the lowest levels

What is noble gas notation?

a shorthand that replaces the inner electrons with the symbol of the previous noble gas in brackets

Why is noble gas notation useful?

it shortens long configurations for atoms with many electrons

How does an element's period (row) relate to its electrons?

the period number tells you the outermost shell being filled

How does an element's group (column) relate to its electrons?

elements in the same group have the same number of valence electrons

How do valence electrons change across a period?

they increase by one from left to right

Why are noble gases so stable?

their outer s and p subshells are full, satisfying the octet rule

Why is argon stable even though its third shell isn't completely full?

its 3s and 3p subshells are full with eight electrons, and the 3d fills only later

Why do the s and p subshells matter most in biology?

most organic chemistry involves electrons in s and p subshells

What is the link between standing waves and orbitals?

orbital shapes come from electrons behaving as standing waves around the nucleus