AdMob - Required XML attr. "adSize" was missing

Hi i'm new at android app. developing. So my errors may seem silly and ridicilous and i'm very sorry about that.

Anyways;

I've been trying to use AdMob for my android app. But I can't. On the graphical layout it says "Required XML attr. "adSize" was missing." I looked other topics but no luck so far. Also my app won't start anymore. It always crashes.

ActivityMain.xml

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
    xmlns:ads="http://ift.tt/1bhZ3VK"
    xmlns:tools="http://ift.tt/LrGmb4"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/radial_background"
    tools:context=".MainActivity" 
    xmlns:app="http://ift.tt/GEGVYd">

    <ImageButton
        android:id="@+id/btnSwitch"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="100dip"
        android:src="@drawable/btn_switch_on"
        android:background="@null"
        android:contentDescription="@null" />
<LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

<com.google.android.gms.ads.AdView android:id="@+id/adView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        ads:adUnitId="MY_AD_ID"
        ads:adSize="BANNER"/>


</LinearLayout>
</RelativeLayout>

MainActivity.java

public class MainActivity extends Activity {
    AdView adView;
   ImageButton buttonSwitches;
    private Camera camera;
    private boolean cek;
    private boolean ciftcek;
    Parameters params;
    MediaPlayer medpl;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    AdView adView = (AdView) this.findViewById(R.id.adView);
    AdRequest adRequest = new AdRequest.Builder().build();
    adView.loadAd(adRequest); //adView 

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://ift.tt/nIICcg"
    package="com.example.myappname"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="17"
        android:targetSdkVersion="20" />
 <uses-permission android:name="android.permission.CAMERA" />
    <uses-feature android:name="android.hardware.camera" />
 <uses-permission android:name="android.permission.INTERNET"/>
  <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <application
        android:allowBackup="true"

        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" 
        android:name="com.google.android.gms.version"
        android:value="@integer/google_play_services_version" >
        <meta-data android:name="com.google.android.gms.version"
        android:value="@integer/google_play_services_version" />
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
       <activity android:name="com.google.android.gms.ads.AdActivity"     android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"
            android:theme="@android:style/Theme.Translucent" />
    </application>

</manifest>

Can you tell me what's wrong with that code?