xyz.com sites opens properly but www.xyz.com gives error. Is it coz of my Vhost Setup ?

I have setup a following VirtualHost Configuration to server my domain name(xyz.com) and subfolder accordingly. The file is as follows

<VirtualHost *:80> ServerAdmin info@socialcosmo.com ServerName socialcosmo.com ServerAlias www.socialcosmo.com

DocumentRoot /var/www/projectheena
<Directory />
	Options FollowSymLinks
	AllowOverride None
</Directory>
<Directory /var/www/>
	Options Indexes FollowSymLinks MultiViews
	AllowOverride All
	Order allow,deny
	allow from all
</Directory>

Alias /blog /var/www/notes
<Directory /var/www/notes>
            Options Indexes FollowSymLinks MultiViews
            AllowOverride All
            Order allow,deny
            allow from all
    </Directory>



Alias /admin /var/www/admin
<Directory /var/www/admin>
            Options Indexes FollowSymLinks MultiViews
            AllowOverride All
            Order allow,deny
            allow from all
    </Directory>



ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
<Directory "/usr/lib/cgi-bin">
	AllowOverride None
	Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
	Order allow,deny
	Allow from all
</Directory>



ErrorLog ${APACHE_LOG_DIR}/error.log

# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
LogLevel warn

CustomLog ${APACHE_LOG_DIR}/access.log combined

</VirtualHost>

When i hit xyz.com or xyz.com/blog, it works properly. But typing www.xyz.com in browser gives me an error saying

Oops! Google Chrome could not find www.socialcosmo.com

Can somebody point me out where i have gone wrong ?