A negatively charged subatomic particle with negligible mass that occupies energy levels (shells) outside the nucleus.
The particles that do the 'dancing'—they're what's involved in bonding and reactions.
Showing a random 20 of 50 problems.
Example 1
challenge
An electron in a hydrogen atom drops from n=3 to n=2, releasing visible red light. Explain qualitatively why the released photon must have a specific (not arbitrary) energy.
Example 2
medium
A neutral atom has 12 protons. How many electrons does Mg2+ have, and what neutral atom has that many electrons?Mg²⁺ has 10 electrons — the same as neon
Example 3
medium
How many electrons does a Cl− ion have if chlorine's atomic number is 17?Cl⁻ has 18 electrons after gaining one; the third shell is full
Example 4
easy
A neutral fluorine atom has 9 protons. How many electrons does it have?
Example 5
easy
Which subatomic particle is most responsible for chemical bonding?
Example 6
medium
Explain why a sodium atom forms Na+ and not Na−.
Example 7
medium
An iron atom has mass ∼56u. Roughly what fraction of that mass comes from its 26 electrons?
Example 8
hard
Calcium loses 2 electrons and chlorine gains 1 electron to form CaCl2. Verify that total electrons are conserved.
Example 9
medium
An atom of silver has 47 protons and 61 neutrons. How many electrons does the neutral atom have, and what is its mass number?
Example 10
easy
Write the electron configuration of a neutral lithium atom (Z=3).
Example 11
challenge
Why is chemistry governed by electrons rather than by protons or neutrons, even though protons define the element?
Example 12
challenge
A species has 10 electrons. List which neutral atom it could be, plus one cation and one anion that are isoelectronic with it.
Example 13
easy
Which subatomic particle is found outside the nucleus of an atom?
Example 14
medium
Which has more electrons, K+ (Z=19) or Cl− (Z=17)?
Example 15
medium
Light is absorbed by an atom when an electron jumps from a lower to a higher energy level. What happens to the electron's energy?
Example 16
medium
How many valence electrons does a neutral phosphorus atom (Z=15) have?The 5 electrons in the highlighted outer shell are the valence electrons
Example 17
medium
An atom gains 2 electrons to become O2−. If neutral oxygen has 8 electrons, how many does the ion have, and how many protons?O²⁻ gains 2 electrons; 10 electrons total, still 8 protons
Example 18
hard
If an electron carries charge −1.602×10−19C, how many electrons make up 1C of charge?
Example 19
easy
When an atom loses an electron, what is the sign of the resulting ion's charge?
Example 20
hard
A monatomic ion contains 36 electrons and has charge +2. Identify the element and write its noble-gas electron configuration.