VOCATIVE CASE

The Vocative case of nouns is used to address people. It is mainly formed with animate nouns (words denoting people and animals) and names of people. Some inanimate nouns in poetic language may also be used in the Vocative case.
Only masculine and feminine nouns in the singular are used to form the Vocative case. For neuter nouns or nouns in plural the Nominative case is used. Foreign origin names normally are not used in the Vocative case.

In the Vocative Case masculine nouns with a stem in a hard consonant add the ending -Е, and with a stem in a soft consonant add the ending -Ю. Masculine nouns with the stem consonant -Г, К, Х, or -Ч in the Vocative case have the ending -У:
студент - студенте
пан - пане
Іван Петрович - Іване Петровичу
Михайло - Михайле
учитель - учителю
Андрій - Андрію
Київ - Києве
ведмідь - ведмедю
хліб - хлібе

Feminine nouns with a hard stem take the ending -О, and with a soft stem -Е,Є, or -Ю:
дівчина - дівчино
Оксана - Оксано
сестра - сестро
земля - земле
Марія - Маріє
Оля - Олю
Україна - Україно