Atomic number is your answer.
Answer:
168.812 g/mol
Explanation:
atomic mass. of Be= 9.012
atomic mass of Br= 79.90
because there is a 2 after Br you double the atomic mass
79.90(2)= 159.8
To find the molar mass add the atomic masses of each element
9.012+159.8=168.812
Number 18 is correct, number 19 is the particles speed up and the substance expands, and number 20 is decrease in volume
The variable X is the effective nuclear charge, and it remains constant down a group.
Discussion:
The effective nuclear charge is referred to as the actual amount of positive (nuclear) charge experienced by an electron in a polyelectronic atom.
The effective nuclear charge experienced by an electron is otherwise called the core charge.
It is mathematically evaluated as the difference in the atomic number and the core electrons. and since elements in the same group have equal number of Valence electrons, the effective nuclear charge is constant down the group.
Read more on effective nuclear charge:
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