Hi Melissa22 sounds like an interesting subject. Well for starters ARP stands for Address Resolution protocol, this as you might expect links the ip address to a mac address. Since it is dependent on the MAC protocol it is more assosiated with the MAC layer of the network stack, then the ip layer(reason 1 mac layer).
now simply, to use the tcp(ip sits ontop of this) protocol layer you must know 2 thinks your mac address and the other machines mac address(yes there are others). Now to find the other machines mac address you do a ARP broadcast with it's ip address in hope it will reply here is a tcpdump
20:06:43.282618 arp who-has 192.168.4.12 tell 192.168.4.10.
So basically since you don't know the 2 mac addresses you cannot use the tcp/ip protocol to find the other mac address(reason 2 cannot use ip with out the mac addresses)
hope that helps