Science 9 Chemistry

What is Neils Bohr’s contribution to the atomic theory?

• Created the atomic theory

• Discovered that the proton had a positive charge

• Discovered the electron

• Created a model of the atom with electrons moving around the nucleus in a fixed orbit

Answer explanation

Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another.

If n = 4, what is the maximum number of electrons that can fit in this shell? Hint: 2n²

• 8

• 18

• 32

• 50

Answer explanation

if n=4, substitute 4 in the equation 2n²

2(4)² = 32

In which region electrons are likely to be found?

• energy sublevels

• atomic orbitals

• principal energy level

• spin

Answer explanation

An atomic orbital describes the position and wavelike behavior of an electron in an atom. A maximum of two (2) electrons, each with its own spin quantum number, will occupy each of those orbitals.

The atomic orbitals are s, p, d, and f.

Which of the following statement is TRUE about the Pauli Exclusion Principle?

• An atomic orbital can hold a maximum of 6 electrons, each with opposite spins.

• An atomic orbital can hold a maximum of 6 electrons, each with the same spin.

• An atomic orbital can only hold a maximum of 2 electrons, each with opposite spins.

• An atomic orbital can hold a minimum of 2 electrons, each with opposite spins.

Which electron configuration belongs to chlorine (Cl) with atomic number 17?

• 1s² 2s² 2p⁶ 3s² 3p⁴                 

• 1s² 2s² 2p⁶ 3s² 3p⁵            

• 1s² 2s² 2p⁶ 3s² 3p⁶            

• 1s² 2s² 2p⁶ 3s² 3p⁷            

What is the number of valence electrons of an atom with an electron configuration of 1s² 2s² 2p³?

• 2

• 4

• 5

• 7

The exponent or superscript in the electron configuration tells us _____.

• the number of positions of that orbital     

• the number of electrons in that orbital

• the number of electrons in the atom

• the distance from the nucleus or level

Answer explanation

Chlorine has 7 valence electrons. How many electrons does chlorine need to gain to have a full outer shell?

• 0

• 1

• 2

• 8

Why do atoms react with one another to form chemical bonds?

• to form a molecule  

• to form compounds

• to produce ions

• to attain stability          

When an atom loses a valence electron, it becomes a(n) ____.

• neutral

• positive

• negative

• polyatomic