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By Alexei Oreskovic

July 19 (Reuters) - Google Inc's core Internet business boosted revenue 21 percent in the second quarter, while its recently acquired Motorola Mobility business raised Google's overall revenue to $12.21 billion.

Google reported second-quarter net income of $2.79 billion, or $8.42 per share, on a consolidated basis.

Shares of Google were up 3 percent at $609 in after-hours trading on Thursday.

The cost per click for Google's online search ads continued to decline in the second quarter, falling 16 percent year-on-year, while the overall number of clicks on its ads increased 42 percent.

Google, the world's No. 1 Web search engine, closed its $12.5 billion acquisition of Motorola in mid-May, giving Google a foothold in the fiercely competitive smartphone hardware business, dominated by companies such as Apple Inc and Samsung.

Google said the revenue at its existing Internet business totaled $10.96 billion in the second quarter, compared with $9 billion in the year-ago period. Revenue at Motorola in the second quarter was $1.25 billion. (Reporting By Alexei Oreskovic; Editing by Steve Orlofsky)