Form inputs with sweet alert and jquery

I have a form with two states. In first state required inputs are fill and in the second state are empty. I use sweet alert to show result of input, but if-else don´t work properly. My form code is

<link rel="stylesheet" type="text/css" href="http://ift.tt/1EUgO2B"/>
       <form method='post'>
            <input type="text" name="nombre" id="nombre" autofocus required placeholder="Escribe tu nombre (Obligatorio)"/>
            <br>
            <input type="mail" name="mail" id ="mail" required placeholder="Escribe tu correo (Obligatorio)">
            <br>
            <input type="tel" name="telefono" placeholder="Escribe tu teléfono" />
            <br>
            <textarea rows="5" cols="35" name="mensaje" id="mensaje" required placeholder="Escribe tu mensaje (Obligatorio)"  /></textarea>
            <br>
            <input type="submit" id="enviar" value="Enviar" />
        </form>

And my jquery code

 <script src="http://ift.tt/1yCEpkO"></script>
 <script src="http://ift.tt/1EUgO2F"></script>
                    $("#enviar").click(function () {
                    if ($("#nombre").is(':empty')){
                        swal({
                            title: "Datos incorrectos.",
                            text: "No se ha enviado el correo.",
                            type: "warning", 
                            allowOutsideClick: false,
                            timer:5000,
                        });
                    }
                if ($("#nombre").not(':empty')){
                 swal({
                    title: "Correcto.",
                    text: "Se ha enviado el correo.",
                    type: "success", 
                    allowOutsideClick: false,
                    timer:5000,

                });
             }
        });

Any idea?