What is the criteria to place an element in a particular group?

Chemistry

1 answer:

emmainna [20.7K]3 years ago

4 0

Answer: The criteria to place elements into groups and periods lies in their atomic number

Explanation:

As we know that period is the horizontal rows of elements in the periodic table and groups are vertical column of elements in the periodic table.

In a period we place those elements that have same number of shells and in a group those elements are placed that have different number of shells and the number of shells increases from top to bottom in a periodic table

For example

Sodium having symbol Na, atomic number of sodium is eleven it's electronic configuration is 1s2,2s2,2p6,3s1, next to it in a period is places potassium having symbol,K, it's electronic configuration is 1s2,2s2,2p6,3s2.

Sodium and potassium both r placed in a period not in a group because both of these have same outer most shell, only the number of electron in outer most shell varies.

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Consider the following reaction:C2H4(g) + F2(g) -----------> C2H4F2(g) Delta H = -549 kJEstimate the carbon-fluorine bond ene

frutty [35]

Answer:

Bond energy of carbon-fluorine bond is 485 kJ/mol

Explanation:

Enthalpy change for a reaction, is given as:

$\Delta H_{rxn}=\sum [n_{i}\times (E_{bond})_{i}]-\sum [n_{j}\times (E_{bond})_{j}]$

Where $(E_{bond})_{i}$ and $(E_{bond})_{j}$ represents average bond energy in breaking "i" th bond and forming "j" th bond respectively. $n_{i}$ and $n_{j}$ are number of moles of bond break and form respectively.

In this reaction, one mol of C=C, four moles of C-H and one mol of F-F bonds are broken. One mol of C-C bond, four moles of C-H bonds and two moles of C-F bonds are formed

So, $-549kJ=(1mol\times 614kJ/mo)+(4mol\times E_{C-H})+(1mol\times 154kJ/mol)-(1mol\times 347kJ/mol)-(4mol\times E_{C-H})-(2mol\times E_{C-F})$