Ch#3 : Periodic Table Flashcards
Learn about the periodic table and the properties of elements.
Why is the periodic table useful?
It is one of the most important tools important tools in Chemistry. It is useful for understanding and predicting the properties of elements. For instance , if you know the physical and chemical properties of one element in a group , you can predict the physical and chemical properties for other elements in the same group. We can use the periodic table to relate trends in the reactivity of elements with their atomic structure. You can also predict whether elements can form ionic or covalent bonds.
What is the periodic table and what is it based on?
A table showing the systematic arrangement of elements is called the periodic table. After the discovery of the atomic number by Moseley in 1913. It was noticed that the atomic number could serve as a base for the systemic arrangement of elements is called the periodic table. It is based on the periodic law/function which states “If elements are arranged in the order of their increasing atomic numbers , their properties are repeated in a periodic manner.”
What are periods and groups? Name Groups 2A , 3A , 7A and 8A
Period : The horizontal row of the periodic table is called a period. There are 7 periods and the no. of elements ranged from 2 in period 1 to 32 in period 6. First 3 periods are short periods and rest are long periods.
Groups : Elements which have similar properties lie in the same column of the periodic table. Each column is called a group or family.
Elements with similar valence shell electronic configuration are placed in the same group. Each group is identified by a number and the letter A or B. Group A elements are called normal/representative/main group elements. Group B elements are called transition elements.
1A : Alkali Metals
2A : Alkaline Earth Metals
7A : Halogens
8A : Noble Gases
What are s and p block elements?
On the basis of the valence sub shell , the period table can be classified into 4 blocks. Group 1A and 2A elements contain their valence electrons in the s-subshell so they are called s-block elements. The elements of Group 3A to 8A(except He) are p block elements because their valence electrons are in the p subshell.
What is the shielding effect? , Describe the trends for it.
Shielding Effect : is the reduction in force of attraction between the nucleas and valence electrons by the electrons in the inner subshells is called the shielding effect.
Trends in group : As we move from top to bottom in a group , the number of electronic shells increases so the number of electrons in the inner sub shells also increases , so the shielding effect increases.
Trends in Period : As we move from left to right ina period. The number of electrons in the inner subshells remains constant so the shielding effect remains constant.
Define atomic size and its trends.
Atomic Size : is the average distance between the nucleas of an atom and the outermost electronic shell.
Trend in Periods : The atomic radius decreases as we move from left to right in a period. This is because an electron is added to the same valence shell when we move across a period but the nuclear charge increases by 1. The attractive force of the nucleas for the valence electrons increases. So the shell size and atomic radius decrease.
Trend in groups : The atomic radius increases in any given main group as we move down the group. This is because the size of an atom is determined by the size of its valence shell. As we move down a group , the atom has an additional shell of electrons so it increases.
What is Ionization energy? , Explain its trends.
Ionization Energy : is defined as the minimun amount of energy required to remove the outermost electron from an isolated gaseous atom.
It is a measure of the extent to which the nucleas attracts the valence electrons. A small Ionization energy indicates a weak force of attraction between the nucleas and electrons and a strong ionization energy indicates a strong force of attraction between the nucleas and the valence electrons. Measured in kJ/Mole.
Trend in groups : Ionization energy decreases as we move from top to bottom in a group. This is because of the shielding effect increasing as we descend down a group. Greater shielding effect results in a weaker force of attraction between the nucleas and the valence electrons so they are easier to remove. This leads to a decrease in ionization energy down a group.
Trends in Periods : As we move from left to right in a period , the shielding effect remains constant and the nuclear charge progressivley increases. The force of attraction between the nucleas and valence electrons increases so the ionization energy increases.
What is electron affinity? Describe its trends.
Electron affinity : is defined as the amount of energy of energy released when an electron adds up in the valence shell of an isolated gaseous aton to form a uninegative gaseous ions.
As you move from left to right across a period , the electron affinity generally increases. This is due to the increase in nuclear charge and decrease in atomic radius , which binds the electron more tightly to the nucleas. But the shielding effect constant in each period so alkali metals have the lowest and halogens have the highest electron affinities in each period.
Trend in Groups : The electron affinity decreases as we move from top to bottom in a group. This is due to the shielding effect. The increased shielding effect causes the electron to bind less tightly to the nucleas and thus less energy is released.
Define Electronegativity and explain its trends.
Electronegativity : is the ability of an atom to attract electrons towards itself in a chemical bond. The american chemist Linus Pauling devised a method for calculating electronegativities of elements.
Trends in Periods : It increases as we move from left to right across a period due to the increase in nuclear charge and decrease in atomic size.The shielding effect remains constant.It increases the atoms ability to attract electrons towards itself.
Trends in Groups : It decreases as we move down a group due to the increase in shielding effect which reduces the atom’s ability to attract electrons.
Difference between normal and transition elements.
Normal : Transition
- s and p block elements : d and f block elements
- Hydrogen , Aluminum , Phosphorus , Carbon and Sodium are normal elements. : Silver , Copper , Tungsten , Gold and Zinc are transition elements.
- They have low densities : They have high densities
- Have fixed valencies e.g Na+1 , Cl-1 : Have varying valencies. e.g Fe+2 , Fe+3
- They have low melting points : High melting points
- They dont form colorful compounds : They form colorful compounds
