explain the size of an atom and some symbols to refer them
Answers
Answer:
The actual trends that are observed with atomic size have to do with three factors. These factors are:
The number of protons in the nucleus (called the nuclear charge).
The number of energy levels holding electrons (and the number of electrons in the outer energy level).
The number of electrons held between the nucleus and its outermost electrons (called the shielding effect).
Lesson Objectives
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Define atomic radius.
State the boundary issue with atomic size.
Describe measurement methods for atomic size.
Define the shielding effect.
Describe the factors that determine the trend of atomic size.
Describe the general trend in atomic size for groups and for periods.
Describe the trend of atomic radii in the rows in the Periodic Table.
Describe how the trend of atomic radii works for transition metals.
Use the general trends to predict the relative sizes of atoms.
Use the concept of effective nuclear charge to explain why the atomic radii of the main group elements increase when we move down a group in the periodic table
Explanation:
Atoms Have No Definite Boundary
Edit
The region in space occupied by the electron cloud of an atom is often thought of as a probability distribution of the electrons and therefore, there is no well-defined "outer edge" of the electron cloud. Atomic size is defined in several different ways and these different definitions often produce some variations in the measurement of atomic sizes.
Because it is so difficult to measure atomic size from the nucleus to the outermost edge of the electron cloud, chemists use other approaches to get consistent measurements of atomic sizes. One way that chemists define atomic size is by using the atomic radius. The atomic radius is one-half the distance between the centers of a homonuclear diatomic molecule (a diatomic molecule means a molecule made of exactly two atoms and homonuclear means both atoms are the same element). The figure below represents a visualization of the atomic size definition.
A visual representation of the atomic radius of a hydrogen atom. The measurement would be taken as one-half the distance between the nuclei of the hydrogen atoms in a diatomic hydrogen molecule.
How do we measure the size of the atom? Ernest Rutherford is famous for his experiments bombarding gold foil with alpha particles. The gold foil experiment by Rutherford, first done in 1911, is of particular interest to us in this unit because it was this experiment that first gave science an approximate measurement for the size of the atom. He was able, using technology available in the early part of the 1900s, to determine quantitatively that the nucleus had an approximate size of 4×10−12 cm. The size of the atom is slightly larger, approximately 2×10−8 cm in diameter.
Atomic Size in a Column Increases from Top to Bottom
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Let's now look at the atomic radii or the size of the atom from the top of a family or group to the bottom. Take, for example, the Group 1 metals. Each atom in this family (and all other main group families) has the same number of electrons in the outer energy level as all the other atoms of that family. Each row (period) in the periodic table represents another added energy level. When we first learned about principal energy levels, we learned that each new energy level was larger than the one before. Energy level 2 is larger than energy level 1, energy level 3 is larger than energy level 2, and so on. Therefore, as we move down the Periodic Table from period to period, each successive period represents the addition of a larger energy level. It becomes apparent that as we move downward through a family of elements, that each new atom has added another energy level and will, therefore, be larger.
Answer:
The actual trends that are observed with atomic size have to do with three factors. These factors are:
The number of protons in the nucleus (called the nuclear charge).
The number of energy levels holding electrons (and the number of electrons in the outer energy level).
The number of electrons held between the nucleus and its outermost electrons (called the shielding effect).
Lesson Objectives
Edit
Define atomic radius.
State the boundary issue with atomic size.
Describe measurement methods for atomic size.
Define the shielding effect.
Describe the factors that determine the trend of atomic size.
Describe the general trend in atomic size for groups and for periods.
Describe the trend of atomic radii in the rows in the Periodic Table.
Describe how the trend of atomic radii works for transition metals.
Use the general trends to predict the relative sizes of atoms.
Use the concept of effective nuclear charge to explain why the atomic radii of the main group elements increase when we move down a group in the periodic table
Explanation:
Atoms Have No Definite Boundary
Edit
The region in space occupied by the electron cloud of an atom is often thought of as a probability distribution of the electrons and therefore, there is no well-defined "outer edge" of the electron cloud. Atomic size is defined in several different ways and these different definitions often produce some variations in the measurement of atomic sizes.
Because it is so difficult to measure atomic size from the nucleus to the outermost edge of the electron cloud, chemists use other approaches to get consistent measurements of atomic sizes. One way that chemists define atomic size is by using the atomic radius. The atomic radius is one-half the distance between the centers of a homonuclear diatomic molecule (a diatomic molecule means a molecule made of exactly two atoms and homonuclear means both atoms are the same element). The figure below represents a visualization of the atomic size definition.
A visual representation of the atomic radius of a hydrogen atom. The measurement would be taken as one-half the distance between the nuclei of the hydrogen atoms in a diatomic hydrogen molecule.