C2 The Periodic Table

Question 1

Dmitri Mendeleev

Answer 1

in 1869 took the 50 or so elements known at the time and arranged them into a version of the periodic table with multiple gaps for unfound elements.
he put them in order of atomic mass. the gaps left predicted undiscovered elements at that time.

Question 2

atomic mass

Answer 2

once protons and electrons were discovered the atomic number of each element could be found based on the number of protons in the nucleus.

Question 3

groups n periods

Answer 3

the modern periodic table shows the elements in order of ascending atomic number fitting in the pattern mendeleev worked out.
the periodic table is laid out so elements with similar chemical properties form columns- called groups.
the group corresponds to the amount of electrons in its outer shell
the rows are called periods, each new period corresponds to the number of shells an electron has