Atomic Size

1. Atomic Size • The atomic radius is one half of the distance between the nuclei of two atoms of the same element when the atoms are joined.

4. Why do these trends exist? • Atom size increases down a group because you keep moving to a new shell of electrons. • It decreases across a period because you keep adding protons to the nucleus, which has a bigger effect than adding an electron.

5. Ions • Positive and negative ions form when electrons are transferred between atoms.

7. Ions • Some compounds are composed of particles called ions. • An ion is an atom or group of atoms that has a positive or negative charge. • A cation is an ion with a positive charge. • An anion is an ion with a negative charge.

8. Ionic Size • Cations are always smaller than the atoms from which they form. Anions are always larger than the atoms from which they form.

9. Trends in Ionic Size Size generally increases

10. Ionization Energy • The energy required to remove an electron from an atom is called ionization energy. • The energy required to remove the first electron from an atom is called the first ionization energy. • The energy required to remove an electron from an ion with a 1+ charge is called the second ionization energy.

13. Trends in Electronegativity • Electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound. Electronegativity Increases Electronegativity Decreases

14. 1. Which of the following sequences is correct for atomic size? • Mg > Al > S • Li > Na > K • F > N > B • F > Cl > Br

15. 2. Metals tend to • gain electrons to form cations. • gain electrons to form anions. • lose electrons to form anions. • lose electrons to form cations.

16. 3. Which of the following is the most electronegative? • Cl • Se • Na • I