chemistry-class-11-unit-03-chapter-01-classification-of-elements-periodicityin-properties-l-1-2-qiflids830k

### <Success style="font-size:25px"> Classification Of Elements And Periodic Properties L-1 </Success>
### <primary style="font-size:24px"> Classification of elements and periodic properties </primary>
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* Positions of elements
* Group wise classification
* Periodic trends - atomic size , electronegativity , electron affinity , ionization enthalpy etc
* Naming the elements

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- Classification of elements into $s, p, d$ and $f$ blocks
- Significance of periodic trends in physical and chemical properties

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* Comparison of reactivity of elements
* Relationship between ionization enthalpy and metallic properties

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- It is a known fact that the elements are the basis units of all types of matter including both living and non-living things

|Number of elements known in|1800 was only| 31 |
| --------                  | --------    | ---|
| Number of elements known in |     1865 was only   | 63 |
|Number of elements known in |     1984 was only    | 107|
|Number of elements known in |     1997 was only   | 112|
|Number of elements known in|     2004 was only   | 114|
|Number of elements known in|     2016 was only   | 118|

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- Out of 118, 90 + 4 (Neptunium , Plutonium , Actinium and Protoactinium are also found along with Uranium in pitch blende) are stable elements and the rest are radioactive

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- In 1800s german chemist Johann Dobereiner - several groups of three elements
- For example -

|  Li  | 7 |  Ca  |  40  |   Cl | 35.5 |
| ---  | - | ---- | -----| ---- |----- |
|   Na | 23|  Sr  |  88  |   Br |  80  |
|   K  | 39|  Ba  |  137 |   I  |  127 |

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- French geologist A. E. B. de Chancourtois in 1862 - arranged known elements in the order of increasing atomic weight and made a cyclindrical table of elements to display then known properties

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- English chemist John Newland in 1865

| Li | Be | B | C | N | O |  F  |
| ---| -- |-- | --| - | - |--   |
| 7  | 9  | 11| 12| 14| 16|  19 |
| Na | Mg | Al| Si| P | S |  Cl |
| 23 | 24 | 27| 29| 31| 32| 35.5|
| K  | Ca | <p style="font-size:20px">Good up to calcium and not fully accepted |
| 39 | 40 | <p style="font-size:20px">Awarded davy medal in 1887 by london royal society |

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* He arranged the elements in increasing order of their At. Wt. and noted every eight element having the properties similar to the first element
* This was called law of octaves
* Interestingly this observation was similar to music notes , example - every eight note being similar to the first in octave of music

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**Mendeleev's 1871 periodic table published in 1905**
 - Dmitri Mendeleev (born: 8 Feb 1834 - died - 2 Feb 1907 $\hspace{0.5mm}$ 72 years)

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| 119 | Ununennium   | Uue |
| --- | ------------ | --- |
| 134 | Untriquadium | Uuq |
| 146 | Unquadhexium | Uqh |
| 158 | Unpentoctium | Upo |

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- If element 119 is discovered what is its electronic configuration ?
- For element with Z = 118 [oganesson]
- It is $[R n] 5 f^{14} 6 d^{10} 7 s^2 7 p^6$
- For element with Z = 119
- It will be $[Og]8s^1$ It will be placed among alkali metals below francium

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| Li z=3 | $\quad 1 s^2 2 s^1$ |
| -------- | -------- |
| Na Z=11    | $1s^2 2s^2 2p^6 3s^1 or [Ne]3 s^1$     |
| K (19)    | $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 4 s^1$ or $[$ Ar $] 4 s^1$    |
| Rb (37)  | $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^{10} 4 s^2 4 p^6 5 s^1$ or $[\mathrm{Kr}] 5 s^1$     |
| Cs (55)   | $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 3 d^{10} 4 s^2 4 p^6 4 d^{10} 5 s^2 5 p^6 6 s^1$ or $[X e] 6 s^1$     |
| Fr (87)    | $1 s^2 2 s^2 2 p^5 3 s^2 3 p^6 3 d^{10} 4 s^2 4 p^6 4 d^{10} 5 s^2 5 p^6 5 d^{10} 4 f^{14} 6 s^2 6 p^6 7 s^1$ or $[R n] 7 s^1$    |

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- The concept of IE and EN in surveying the periodic trends in the properties of the oxides , chlorides and hydrides of the main group elements 
- The use of VSEPR in predicting the basic molecular shapes , and basic molecular orbital (MO) theory for describing the bonding in diatomic molecules

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- Ionization energies $(kJ mol^{-1})$

| Element | K | Al |
| -------- | -------- | -------- |
| First IE    | +425     | +584     |
| Second IE    | +3058     | +1823     |
| Third IE    | +4418     | +2751     |

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- First ionization energies for the elements Li to Ca
- The 'kinks' in the ionization energy plot at ' B ' and `O' can be explained by electronic configuration

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- Second ionization energy (enthalpy) for elements Li to Na (relative trend shown for first ionization energy-not to scale)

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- **Trends are same in both I and II IE**

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| First electron affinities (kJ $mol^{-1}$) |  | 
| -------- | -------- | 
| F     |  -322    | 
| Cl    |  -349    | 
| Br    |  -325    | 
| l     |  -295    |

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- Increasing non-metallic character
- Main group elements can be roughly classified as metals with an electronegativity $<2$, as non-metals with electronegativities $>2.2$
- Increasing metallic character

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- $H^{\delta+}-X^{\delta-}$

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- Predict the properties of the hydrides formed by elements with electronegativities of (i) 0.9 and (ii) 3.5

- An element with EN of 0.9 is a metal - it will probably form an ionic hydride which will react with water , giving hydrogen and a basic solution of the hydroxide
- This is a non-metal, and the hydride will be covalent with a polar $\mathrm{H}-\mathrm{X}$ bond and will dissolve in water , probably giving a neutral acidic solution

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- $Na_2O+H_2O \rightarrow 2Na^++2OH^- \hspace{2mm} 2NaOH$
- $CaO+H_2O \rightarrow Ca^{+2}+2OH^- \hspace{2mm} Ca(OH)_2$
- $SO_3+H_2O \rightarrow H_2SO_4 \rightarrow 2H^++SO_4^{2-}$
	
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