Early Models of the Atom
Who first suggested that matter is made of tiny particles called “atomos” (indivisible)?
Democritus
What subatomic particle has a positive charge?
Proton
What does the atomic number of an element represent?
The number of protons in an atom.
Who created the first periodic table by arranging elements by mass?
Dmitri Mendeleev
This element has 1 energy level and 1 valence electron.
Hydrogen (H)
Which scientist proposed the first modern atomic theory in 1803?
John Dalton
Which subatomic particle has no charge?
Neutron
An element has an atomic number of 11 and an atomic mass of 23. How many neutrons does it have?
12 neutrons
Who reorganized the periodic table by atomic number, giving us the modern version?
Henry Moseley
This element has 2 energy levels and 8 valence electrons.
Neon (Ne)
Which scientist discovered the electron?
J. J. Thomson
Where are electrons located in an atom?
In energy levels / electron clouds around the nucleus (outside the nucleus)
Carbon has two main isotopes: Carbon-12 (98.9%) and Carbon-13 (1.1%). Calculate its average atomic mass.
12.01 amu or g
What do all elements in the same family have in common?
They have the same number of valence (outer-shell) electrons.
This element has 3 energy levels and 2 valence electrons.
Magnesium (Mg)
Who conducted the gold-foil experiment and discovered the nucleus?
Ernest Rutherford
Who discovered the neutron?
James Chadwick
An element has an atomic number of 26 and a mass number of 56. Find the number of neutrons. Then name the element.
Neutrons = 56 − 26 = 30 neutrons, element = Iron (Fe)
What do elements in the same period have in common?
They have the same number of energy levels (shells).
This element has 4 energy levels and 7 valence electrons.
Bromine (Br)
Which scientist developed the electron cloud model?
Erwin Schrödinger
Why don’t protons in the nucleus fly apart even though they repel each other?
Because neutrons bind protons together, overcoming the repulsion between protons - Neutrons act like superglue between protons.
Silicon has three naturally occurring isotopes:
Si-28 with a mass of 27.98 amu (92.23%)
Si-29 with a mass of 28.98 amu (4.67%)
Si-30 with a mass of 29.97 amu (3.10%)
Calculate the atomic weight of silicon.
28.10 amu or g
Why are we choosing to not focus on the middle section of the periodic table?
This element has 3 energy levels and 5 valence electrons.
Phosphorus (P)