Presentation on theme: " Size is expressed in terms of atomic radius. Atomic radius is ½ the distance between the nuclei of two atoms of the same element when the atoms are."— Presentation transcript:
Size is expressed in terms of atomic radius. Atomic radius is ½ the distance between the nuclei of two atoms of the same element when the atoms are joined. In general, atomic radius increases from top to bottom within a group and decreases from left to right across a period.
Two changes as atomic number increases as you go down a group… The charge on the nucleus increases, drawing electrons and closer to the nucleus, and… The number of occupied energy levels increases, with occupied orbitals shielding electrons in the highest occupied energy level from the attraction of protons in the nucleus.
The shielding effect is greater than the attractive force of the nucleus, so atomic size increases.
Within a period, size decreases from left to right. As protons are added across the period, the electrons in the same principal energy level are pulled closer to the nucleus. Since the shielding effect is constant for all elements in a period, atomic size decreases across the period.
An ion is an atom or group of atoms that has a positive or negative charge. Atoms are electrically neutral ….the number of protons equals the number of electrons. Positive and negative ions form when electrons are transferred between atoms. A cation is a positively charged ion. It has lost one or more electrons, so it has more protons than electrons, and a net positive charge. Na 1+
An anion is a negatively charged ion. It has gained one or more electrons. With more electrons than protons, it has a negative charge. Cl 1-
Ionization energy is the energy required (measured in the gaseous state) to remove an electron from an atom. The energy required to remove the first electron from an atom, forming a cation with a 1+ charge, is called the first ionization energy. First ionization energy tends to decrease from top to bottom within a group, and increase from left to right across a period.
First ionization energy generally decreases from top to bottom within a group. Since atomic size increases down the group, the nucleus’ charge has a smaller effect on the electrons in the highest occupied energy level.
First ionization energy generally increases from left to right across a period. As the nuclear charge increases, the shielding effect remains constant. The electrons have a greater attraction for the nucleus, so it takes more energy to remove an electron from an atom.
Cations are always smaller than the atoms from which they are formed. Anions are always larger than the atoms from which they are formed.
Electrons are involved in the bonding of ions to form compounds. Electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound. In general, electronegativity values decreases from top to bottom within a group, and, for representative elements, the values tend to increase from left to right across a period.
The least electronegative element is cesium, with the least tendency to attract electrons (0.7). The most electronegative element is fluorine (4.0).