Spanish Adjectives

• Spanish Adjectives: Part I

most adjectives change form, depending upon whether the word they modify is masculine or feminine. Notice the difference between “the tall boy” and “the tall girl.”
    el chico alto
    la chica alta

Adjectives also change form depending upon whether the word they modify is singular or plural. Notice the difference between “the tall boy” and “the tall boys” ; “the tall girl” and “the tall girls.”
Notice how the endings of the nouns and these adjectives are similar

    el chico alto
    los chicos altos

Adjectives that end in -e also change form for singular or plural. To form the plural, simply add -s.
la chica inteligente
las chicas inteligentes

Adjectives that end in -e do not, however, change form for masculine or feminine
la chica inteligente
el chico inteligente

most adjectives that end in a consonant do change form for singular or plural, but do not change for masculine or feminine. To form the plural, add -es.

    la chica popular
    el chico popular

http://studyspanish.com/grammar/lessons/adj1

• Adjectives: Part II

Many adjectives of nationality end in -o. These adjectives follow the same rules as other adjectives ending in -o. That is, they have four forms.

    el muchacho mexicano
    la muchacha mexicana

    los muchachos mexicanos
    las muchachas mexicanas

Many other adjectives of nationality end in a consonant.
    el muchacho español
    la muchacha española

    los muchachos españoles
    las muchachas españolas


There is another group of adjectives that does not follow the normal rules. Adjectives ending in -or, -án, -ón, or -ín also have a feminine form
el chico hablador
la chica habladora

los chicos habladores
las chicas habladoras

Adjectives that are descriptive usually follow the noun they describe.
    el chico alto

Adjectives of quantity almost always come before the noun. Such adjectives tell how much or how many.
    pocos libros

Sometimes, a descriptive adjective can precede the noun. If the adjective is descriptive, but speaks of a quality that is inherent and usually taken for granted, the adjective comes first.
    la blanca nieve
    the white snow (snow is inherently white)


http://studyspanish.com/grammar/lessons/adj2