How to get the object to move only when I click on it and not just anywhere else?

Hi everyone i was trying to make a 2D game where mt gameobject(key) moves when I click on it.Well I was able to move it using the c# script below but, the problem is that when I add more than one object and when i click they all move at once. I just want them to move only I click on them and not just anywhere else on the screen not even on any other object.
Please note that I am not using Transform since I am dealing with collisions and I don’t my object to shake on collision .
using UnityEngine;
using System.Collections;

public class movement2 : MonoBehaviour {

	void Start () {

	void Update () {
		if (Input.GetMouseButton(0)) {
			GetComponent<Rigidbody2D>().AddForce (new Vector2(-3,0));

If you place the script on each GameObject you want to drag, you can use OnMouseOver() it’s getting called on the GameObject, when the mouse is over it.