Chapter # 2. Atomic structure

Vocabulary

English	Українська назва	English	Українська назва
Nucleus	Ядро	Spin	Спін (електрону)
Proton	Протон	Unpaired (paired) electrons	Неспарені (спарені) електрони
Neutron	Нейтрон
Quantum of energy	Квант енергії	Ground state	Стаціонарний (незбуджений) стан атому
Oxidation number	Ступінь окислення
Orbit	Oрбіта	Excited state	Збуджений стан
Quantum figure	Квантове число

Sourses:

1. Introduction in General, Organic and Biochemistry, 7^th Edition, by Morris Hein, Leo R. Best, Scott Pattison and Susan Arena, Brooks/Cole Publishing Co., 2001. (Chapters 3, 4, pp. 70-125);

2. http://www.shodor.org/UNChem/basic/atom/index.html

3. http://library.thinkquest.org/3616/chem/Atom.htm

4. http://www.tannerm.com/bohratom.htm

5. http://www.ucdsb.on.ca/tiss/stretton/chem1/elecon6.htm

6. http://library.thinkquest.org/3659/structures/shapes.html

7. http://www.tannerm.com/orbitals.htm

1. General notions

Atom is an electroneutral particle consisted of positive charged nucleus and negative charged electrons. Nucleus is a positive charged component of atom concentrated practically all its mass. Components of nucleus are s (р) and s (n). Sum of protons and neutrons is equal to relative atomic mass (A_r):

A_r = p⁺+n⁰

Nucleus charge of atom is equal to number of element in Periodical Table (Z):

Example: To consider structure of atom Na:

Z (Na) = 11

A_r(Na)=23

Positive charge of atomic nucleus – 11

Number of electrons - 11

In nucleus: p⁺-11

n⁰-12 ( A_r - p⁺)

2. Theories of atomic structure

Historically development of ideas about atomic structure passed some stages:

• Concept of G.G. Thompson (sometimes named theory of “pudding with raisins”). Practically it was the first scientific theory, which described an atom as continuous positive charged continuum of nucleus with dissemination of little negatively charged electrons. This theory was destroyed after the experiments made by Sir Reserford using α-particles (nuclear of helium) bombed metallic foils. It was determined that the most of particles passed over foils without any changes. It means that nucleus is not a continuous continuum.

• Reserford’s theory was based on the idea that atomic structure is similar to Solar system (another name of this theory is “planetary”). According to this theory atom consists of massive compact nucleus and electrons turned around it like planets around the Sun. But this idea mismatched to the concepts of classic electrodynamics (Maxwell’s theory). In accordance with one moving electron must loss energy uninterruptedly and finally fall on nuclear. But in reality atoms and all world exist without serious problems. Danish outstanding scientist N. Bore improved planetary theory using some concepts called postulates of Bore. He proposed that electron does not radiate energy when moving on so-called “stable” orbits. Energy can radiates or absorbs when electron jumps from one orbit to another by separated portion - quantum of energy. B

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  ut it turned out, that Bore’s theory is valid absolutely only for atom of Hydrogen. The cause of this is in mechanistic approach to the nature of electron. Electron according to Bore’s theory is like a very small boll. But further development of natural science in particular Einstein’s research shows that micro-world have other laws than macro-world.

• Modern theory proceeds from the assumption that electron combines the property of physical body and electromagnetic wave. And therefore it is necessary to use other notion for describing of electron moving around nucleus – electronic orbital. Electronic orbital is the part of space where the probability of electron being is 90% or where electron spends 90% of time. Schematically electronic orbital can be described by Fig. 2:

Nucleus

Figure 2. Scheme of Electron orbital

Motion of electrons around nucleus is described by energy and structure of atomic orbital. State of electron is described by values of 4 quantum figures (Tables 3, 4).

Table 3. Names and physical content of quantum figures

Names	Symbol	What’s determined?	Possible values
Main (Principal)	N, n	Orbital energy (main energy level)	Algebraic integers from 0 to ∞ (infinity)
Secondary (Azimutal)	L	Orbital form (energy sub-level)	Algebraic integers from 0 to n-1
Magnetic	ml	Spatial orientation of orbital	From –l to +l (ml=2l+1)
Spin	ms	Own magnetic moment of electrons	+ ½ and - ½

_{Table 4. Schematic description of atomic orbital}

l		ml	Quantity of orbitals	Schematic imagination
0	s	0	1
1	p	-1 0 +1	3
2	d	-2 –1 0 +1 +2	5
3	f	-3 –2 –1 0 +1 +2 +3	7

Example: To show a p-orbital:

l=1, m_l= -1; 0; +1;

p-orbital has 3 variants of space orientation: